chapter 2 single-gene inheritance chapter 2 single-gene inheritance
TRANSCRIPT
![Page 1: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/1.jpg)
CHAPTER 2Single-Gene Inheritance
CHAPTER 2Single-Gene Inheritance
![Page 2: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/2.jpg)
CHAPTER OUTLINE
2.2 Single-gene inheritance patterns
2.3 The chromosomal basis of single-gene inheritance patterns
2.1 Genes and chromosomes
2.5 Sex-linked single-gene inheritance patterns
2.6 Human pedigree analysis
![Page 3: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/3.jpg)
Single-gene inheritance patterns
![Page 4: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/4.jpg)
Chapter 2 Opener
The monastery of the father of genetics, Gregor Mendel
![Page 5: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/5.jpg)
Figure 2-9
The seven phenotypic pairs studied by Mendel
![Page 6: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/6.jpg)
Figure 2-10
Cross-pollination and selfing are two types of crosses
![Page 7: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/7.jpg)
Figure 2-11
Mendel’s crosses resulted in specific phenotypic ratios
![Page 8: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/8.jpg)
Table 2-1
![Page 9: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/9.jpg)
Figure 2-12
A single-gene model explains Mendel’s ratios
![Page 10: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/10.jpg)
Mendel’s explanation:
1. Existence of genes – hereditary determinants of a particulate nature.
2. Genes are in pairs – alternative phenotypes of a character or trait are determined by different forms of a single type of gene – alleles.
3. Principle of segregation – members of the gene pair separate equally into gametes.
4. Gametic content – each gamete carries only one member of each gene pair.
5. Random fertilization – union of one gamete from each parent to form the offspring
![Page 11: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/11.jpg)
Questions about heredity answered by Mendel:
1. What is inherited?alleles of genes
2. How are they inherited?according to principles of segregation and independent assortment
3. What is the role of chance?for each individual, inheritance is determined by chance,but within a population this chance operates in a contextof strictly defined probabilities
![Page 12: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/12.jpg)
The chromosomal basis of single-gene inheritance patterns
![Page 13: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/13.jpg)
Figure 2-13
Stages of the asexual cell cycle
![Page 14: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/14.jpg)
Figure 2-14
Cell division in common life cycles
![Page 15: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/15.jpg)
Figure 2-15
Key stages of meiosis and mitosis
![Page 16: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/16.jpg)
Box 2-1
Stages of Mitosis
![Page 17: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/17.jpg)
Box 2-2
Stages of Meiosis
![Page 18: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/18.jpg)
Figure 2-17
Demonstration of equal segregation within one meiocyte in the yeast S. cerevisiae
![Page 19: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/19.jpg)
Figure 2-18
DNA molecules replicate to form identical chromatids
![Page 20: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/20.jpg)
Figure 2-19
Nuclear division at the DNA level
![Page 21: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/21.jpg)
Genes and chromosomes
![Page 22: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/22.jpg)
Figure 2-2
The nuclear genome
![Page 23: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/23.jpg)
Figure 2-3
A diploid genome visualized
![Page 24: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/24.jpg)
Figure 2-4a
Chromosomal DNA is wrapped around histones
![Page 25: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/25.jpg)
Figure 2-4b
Chromosomal DNA is wrapped around histones
![Page 26: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/26.jpg)
Figure 2-5
Chromosomal condensation by supercoiling
![Page 27: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/27.jpg)
![Page 28: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/28.jpg)
Progressive levels of chromosome packing1. DNA winds onto nucleosome spools2. The nucleosome chain coils into a solenoid3. Solenoid forms loops, and the loops attach to a central scaffold4. Scaffold plus loops arrange themselves into a giant supercoil
![Page 29: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/29.jpg)
Visible chromosome landmarks
![Page 30: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/30.jpg)
Chromosome number
Highest known diploid chromosome numberIndian fern Ophioglossum reticulatum (2n = 1260)
![Page 31: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/31.jpg)
Chromosome sizeand type
![Page 32: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/32.jpg)
![Page 33: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/33.jpg)
![Page 34: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/34.jpg)
Heterochromatin and euchromatin
Feulgen stain
Heterochromatin – densely staining region (more condensed)
Euchromatin – poorly staining region (contains most of the active genes)
![Page 35: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/35.jpg)
Centromeres
Location of satellite DNA in mouse chromosomes
![Page 36: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/36.jpg)
Telomeres
![Page 37: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/37.jpg)
Banding patterns
G-banding chromosomes of a human female (staining with Giemsa reagent)
![Page 38: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/38.jpg)
Enlargement of chromosome 13
![Page 39: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/39.jpg)
Labeling for G bands of chromosome 13
![Page 40: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/40.jpg)
Landmarks that distinguish the chromosomes of corn
Features such as size, arm ratio, heterochromatin, number and position of thickenings, number and location of nucleolar organizers, and banding patternidentify the individual chromosomes within the set that characterizes a species
![Page 41: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/41.jpg)
Figure 2-6
Some landmarks of tomato chromosome 2
![Page 42: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/42.jpg)
Figure 2-7
Representative chromosomal landscapes
![Page 43: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/43.jpg)
Figure 2-8
A specific human chromosomal landscape
![Page 44: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/44.jpg)
Sex-linked single-gene inheritance patterns
![Page 45: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/45.jpg)
![Page 46: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/46.jpg)
A dioecious plant species – Osmaronia dioica
![Page 47: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/47.jpg)
A dioecious plant species – Aruncus diocius
![Page 48: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/48.jpg)
Model Organism: Drosophila
Model Organism Drosophila
![Page 49: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/49.jpg)
Model Organism: Drosophila
Model Organism Drosophila
![Page 50: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/50.jpg)
Figure 2-25
Human sex chromosomes
![Page 51: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/51.jpg)
Figure 2-26
Red-eyed and white-eyed Drosophila
![Page 52: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/52.jpg)
Figure 2-27
An example of X-linked inheritance
![Page 53: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/53.jpg)
Combining probabilities
Product rule When two independent events occur with the probabilities p and q respectively, then the probability of their joint occurrence is pq. If the word "and" is used or implied in the phrasing of a problem solution, a multiplication of independent probabilities is usually required.
Example: In test crossing a heterozygous black guinea pig (Bb x bb), let the probability of a black (Bb) offspring be p = 1/2 and of a white offspring be q = 1/2. The combined probability of the first two offspring being white (i.e. the first offspring is white and the second offspring is white) = q x q = q2 = (1/2)2 = 1/4.
Problem: What is the probability of getting 6(Red) 6(Green) 6(Blue) when all three dice are rolled at the same time? Each dice has six sides and the probability of obtaining any one side is 1/6. So the combined probability in the present example is 1/6 x 1/6 x 1/6 = 1/216.
![Page 54: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/54.jpg)
Sum rule Mutually exclusive events are those in which the occurrence of any one of them excludes the occurrence of the others. The word "or" is usually required or implied in the phrasing of problem solutions involving mutually exclusive events, signaling that an addition of probabilities is to be performed.
Example: With two dice, what is the probability of getting either two 4s or two 5s? The probability of getting two 4s is 1/6 x 1/6 = 1/36. The probability of getting two 5s is 1/6 x 1/6 = 1/36. The probability of getting two 4s or two 5s is 1/36 + 1/36 = 1/18.
Problem: What is the probability of getting two 6s and one 5 on any dice when three dice (Red, Green, Blue) are rolled at the same time? Three ways to get two 6s and one 5: 6R, 6G, 5B = 1/6 x 1/6 x 1/6 or + 6R, 5G, 6B = 1/6 x 1/6 x 1/6 or + 5R, 6G, 6B = 1/6 x 1/6 x 1/6 = 3/216 = 1/72.
![Page 55: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/55.jpg)
Human pedigree analysis
![Page 56: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/56.jpg)
Pedigree Analysis
- pedigree analysis is a scrutiny of records of matings
- pedigrees use standard sets of symbols to depict family trees and lineages
- pedigrees provide concise and accurate records of families
- pedigrees are helpful in following and diagnosing heritable traits (for example, diseases and medical conditions) by describing patterns of inheritance
- pedigrees are useful in mapping (locating and isolating) genes “responsible” for certain traits
![Page 57: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/57.jpg)
Pedigree construction
- use standard set of symbols
- one generation per row (oldest at the top)
- siblings are shown in order of birth (from left to right)
- generations are given Roman numerals (I, II, III, IV, etc)
- individuals within a generation (row) are given Arabicnumerals (1, 2, 3, 4, etc)
![Page 58: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/58.jpg)
Figure 2-28
Pedigree symbols
![Page 59: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/59.jpg)
Analyzing pedigrees
- trial and error: consider one pattern of inheritance at a time for each mating in the pedigree and try to find evidence against it; repeat foreach pattern of inheritance, for example, autosomal recessive or dominant, X-linked recessive or dominant, etc
- patterns of inheritance follow Mendelian rules; Mendelian ratios are rarely observed
- assumption: for rare traits unaffected people entering into a familypedigree (for example, by marriage) are considered homozygousnormal
- result: pedigrees can frequently rule out, but not necessarily prove,a certain pattern of inheritance
![Page 60: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/60.jpg)
I
II
III
IV
Autosomal recessive
- the trait is found equally in both males and females- affected individuals usually have unaffected parents- the pattern of inheritance is often horizontal with several generations
of unaffected individuals, but then several siblings in one generationare affected
![Page 61: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/61.jpg)
I
II
III
IV
Autosomal dominant
- the trait is found equally in both males and females- every affected individual has at least one affected parent- trait shows vertical pattern of inheritance, that is affected
males and females are observed in each generation
![Page 62: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/62.jpg)
Figure 2-30
Pseudoachondroplasia phenotype
![Page 63: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/63.jpg)
Figure 2-31
Inheritance of an autosomal dominant disorder
![Page 64: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/64.jpg)
Figure 2-32
Late onset of Huntington disease
![Page 65: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/65.jpg)
Figure 2-33a
Polydactyly
![Page 66: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/66.jpg)
Figure 2-33b
Polydactyly
![Page 67: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/67.jpg)
I
II
III
IV
X-linked recessive
- more males than females are affected- all the sons of an affected mother will be affected- half the sons of a carrier mother will be affected- all daughters of carrier mothers will be normal, but half will be carriers- affected males do not transmit the trait to their sons- trait often skips a generation
![Page 68: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/68.jpg)
Figure 2-36
Inheritance of an X-linked recessive disorder
![Page 69: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/69.jpg)
Figure 2-37a
Inheritance of hemophilia in European royalty
![Page 70: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/70.jpg)
I
II
III
IV
X-linked dominant
- trait observed in both males and females- affected males ALWAYS transmit the trait to their daughters, but to
NONE of their sons- affected females will transmit the trait to both sons and daughters- trait does not skip generation
![Page 71: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/71.jpg)
Figure 2-39
Inheritance of an X-linked dominant disorder
![Page 72: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/72.jpg)
I
II
III
IV
Y-linked
- only males are affected- the trait is passed from an affected father to all of his sons
![Page 73: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/73.jpg)
Figure 2-40
Hairy ears: a phenotype proposed to be Y linked
![Page 74: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/74.jpg)
Sex-influenced and Sex-limited Traits Not due to X-linked genesDue to autosomal genes expression influenced by sex hormones
both parents contribute equally to offspringno notable mother-to-son or father-to-daughter patterns
example: pattern baldness – sex-influenced traitalleles B and B’B for bald B’ for nonbaldB > B’ in males, B’ > B in femalesgenotype BB --- bald in both sexesgenotype BB’ --- bald in males, nonbald in femalesgenotype B’B’ -- nonbald in both sexes
There are also traits that are sex-influenced, which means that their expression is influenced by the individual's sex. This does not imply that the gene is sex-linked. A human example is pattern baldness. The gene's expression is influenced by hormonal levels and only one copy of the baldness allele is sufficient to cause baldness in a man, whereas two copies are needed in a woman. In effect, it behaves as a dominant in males and as a recessive in females. Though half the sons of a female carrier will be affected, a heterozygous male will also pass the trait to half his sons. Thus, any trait that appears more frequently in males than females is suspect as either sex-linked or sex-influenced. If it is passed from the father or the mother to half the sons, it is likely sex-influenced. If it seems to skip a generation and the pattern is grandfather to grandson, it is likely sex-linked.
![Page 75: CHAPTER 2 Single-Gene Inheritance CHAPTER 2 Single-Gene Inheritance](https://reader035.vdocument.in/reader035/viewer/2022081419/56649e595503460f94b53580/html5/thumbnails/75.jpg)
I
II
III
IV
Mitochondrial inheritance
- both males and females are affected- the trait is passed from an affected mother to all her progeny- affected males do not transmit the trait to any of their progeny