honors biology ch. 9 notes “genetics”974029863910305265.weebly.com/uploads/3/0/7/6/3076138/...p...

Ms. Fairbanks of 10 11/13/11 [email protected] www.science4warriors.com http://www.mybiology.com

honors biology ch. 9 notes “genetics” Mendel’s Laws 9.1 Describe pangenesis theory and the blending

hypothesis. Explain why both ideas are now rejected. Pangenesis: ✍ The ancient Greek physician, Hippocrates (460-370 b.c.),

said ✍ particles called pangenes travel from each part of an

organism’s body to the eggs or sperm and are then passed to the next generation

✍ moreover, changes that occur in the body during life are passed on.

Blending: ✍ Early 19th century ✍ Offspring inherit traits from both parents. ✍ Hereditary materials contributed, mix in forming the

offspring ✍ Like blue and yellow make green ✍ Remain inseparable like green Rejected: ✍ Gametes are not made up of particles of body cells. ✍ Changes in body cells do not affect gametes. ✍ Does not explain how traits missing in one generation

show up in the next. 9.2 Explain why Mendel’s decision to work with peas was a good choice. Gregor Mendel ✍ 1860’s ✍ Austrian Monk ✍ University of Vienna ✍ Physics, math (incl. statistics), chemistry ✍ Published a paper in 1866

o Parents pass on discrete heritable factors (genes)

o Heritable Factors retain individuality generation to generation.

o You can mix colored marbles but they don’t blend their colors.

o Paper discovered 50 years later, simultaneously, by two researchers working independently who each came to the same conclusions as Mendel

✍ Success: o experimental approach o choice of organism o choice of characters used

Garden Pea ✍ short generation times ✍ produced large numbers of offspring from each mating ✍ came in many readily distinguishable varieties ✍ crosses could be strictly controlled due to flower anatomy ✍ typically self-fertilize due to closed petals around

pistil/anther


Terms characteristic : trait ::

gene : allele :: height : short

9.2 Define and distinguish between true-breeding organisms, hybrids, P generation, F1, F2. true-breeding: sexual reproduction produces offspring with inherited traits identical to those of the parents. Homozygous, RR or rr. hybrids: The offspring of two parents that differ in one or more inherited traits; heterozygous, (Rr). P generation: Mendel’s true-breeding parental generation P = RR x rr F1 generation: First Filial (family): the result of Mendel’s Parental cross, will always be a hybrid.

P = RR x rr F1 = all Rr F2 generation: Second Filial: the result of crossing two F1’s.

P = RR x rr F1 = all Rr F2 = 1RR: 2Rr: 1rr

Rr meiosis 2nn

R r R RR Rr

Rr r Rr rr

9.3 Define and distinguish between the following pairs of terms: genotype: genetic make-up, use letters, RR phenotype: expressed, physical traits, use words: red dominant allele: the allele that determines appearance, use capital letters. recessive allele: the allele that is not expressed in the presence of a dominant allele (Rr). This allele is only expressed in the absence of the dominant allele, rr = white, use lower case letters. heterozygous: having two different alleles for a gene: Rr homozygous: having one kind of allele for a gene: RR or rr. monohybrid cross: Following the cross of just one trait at a time. Punnett square: A box format used to show the different possible combinations of gametes in offspring. 9.3 Explain how Mendel’s Law of Segregation describes the inheritance of a single characteristic. A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes.


This explains how a trait can disappear in one generation and reappear in the next generation. Blending of alleles does not occur and each allele retains its ability to encode it’s trait. (see Activity online) 9.4 Describe the genetic relationship between homologous chromosomes. They carry genes for the same characteristic at the same loci on the chromosomes. The genes may be different alleles. One homologue comes from one parent and the other homologue comes from the other parent. 9.5 Explain how Mendel’s law of independent assortment applies to a dihybrid cross. see BioFlix online 9.5 Illustrate this law with examples from Labrador retrievers. 9.5 Illustrate Independent Assortment on your own with examples from Mendel’s work with peas. Use the information on p.155. 9.6 Explain how a testcross is performed to determine the genotype of an organism. If the genotype of an organism with a dominant characteristic is unknown, cross it with an individual that has the recessive trait. It will be homozygous for the trait.


A cross with a heterozygote will reveal the recessive trait in ½ of the offspring. If no recessives are created (after many offspring are produced), the unknown genotype is homozygous dominant. 9.7 Explain how and when the rule of multiplication and the rule of addition can be used to determine the probability of an event. ✍ The probability scale ranges from 0 to 1. ✍ An event that is certain to occur has a probability of 1. ✍ An event that is certain not to occur = 0. ✍ The probability of all events must add to 1. ✍ examples:

✍ tossing a coin and getting heads = ½ ✍ tossing a coin and getting tails = ½

✍ Drawing a jack of diamonds = 1/52 ✍ Drawing any other card = 51/52

o Each toss of a coin is independent of the next toss. o If two coins are tossed simultaneously, they are

independent. o A compound event is the probability of two independent

events coming up with the same result. Rule of multiplication: ✍ To figure probability of compound events. ✍ Example: What is the probability of getting both heads. ✍ ½ x ½ = ¼ ✍ By multiplying fractions you are saying that it is less likely

to happen because the number gets smaller. Rule of Addition: ✍ If there is more than one way to get a combination, use the

rule of addition. ✍ Example: What is the probability of getting one head and

one tail? (Hint: you can toss head/tail OR tail/head and get the combination.)

✍ (½ x ½) + (½ x ½) = ½ ✍ ¼ + ¼ = ½ ✍ By adding together the chances of each coin coming up

one way and then adding it to the probability that they will come up the other way, you are saying that it is more likely to happen because adding fraction makes a bigger number.

On your own:


A plant of genotype AABbCC is crossed with an AaBbCc plant. What is the probability of an offspring having the genotype AABBCC? What is the probability of an offspring having the genotype AaBbCC How about: AABbcc? 9.7 Explain why Mendel was wise to use large sample sizes in his studies. Statistics requires that a sample size that is large enough to avoid individual anomalies from changing the results must be used. 9.8 Explain how family pedigrees can help determine the inheritance of many human traits. Because we can’t control human matings, geneticists must analyze the results of matings that have already occurred. The diagram of this information is called a family tree or pedigree. Symbols are used in a pedigree. normal male = affected male = normal female = affected female = mating/marriage = offspring of a mating in order of birth L to R

A= 1 x ½ = ½ B= ½ x ½ = ¼ C= 1 x ½ = ½ ½ x ¼ x ½ = 1/16

AaBbCC 1 x ½ = ½ (½ x ½) + (½ x ½) = ½ ½ x 1 = ½ ½ x ½ x ½ = 1/8

AABbcc 1 x ½ = ½ (½ x ½) + (½ x ½) = ½ 0 x ½ = 0 ½ x ½ x 0 = 0


9.9 Explain how recessive and dominant disorders are inherited. Provide examples of each. table 9.9 p.163 Recessive Disorders ✍ Most human genetic disorders are recessive. ✍ Most recessive who have recessive disorders are born to

normal parents who are both heterozygous or carriers of the recessive allele. What is P?

✍ Most common fatal genetic disease in the US is cystic fibrosis. (CF).

o Carried by 1/25 people of European ancestry. o Excessive excretion of mucus from lungs,

pancreas, other organs. o Interferes with breathing.

✍ Disorders not evenly distributed due to prolonged geographic isolation.

✍ Example: o Martha’s vineyard (early inhabitants isolated

there) o led to frequent marriages between close

relatives. o Frequency of an allele that causes deafness was

high o deafness allele was rarely transmitted to

outsiders. Dominant Disorders ✍ Caused by one dominant allele. ✍ Examples:

o Polydactyly o Webbed fingers and toes o achondroplasia: one form of dwarfism o Huntington’s disease: symptoms appear after

reproductive years. P = ½ that offspring will inherit.


9.10 Fetal Testing

DESCRIPTION HEALTH RISKS ADVANTAGES DIS-

ADVANTAGES

AMNIO- CENTESIS

14-20 wks gestation, Needle inserted to withdraw 10ml of amniotic fluid which

surrounds the baby. Karyotype after several weeks.

Maternal bleeding Miscarriage

Premature birth Complication rate=1%

Very early in gestation Chromosomal abnormalities

Identified ex. trisomies Other biochemical tests can

be performed with cells to ID Tay-Sachs for example.

Must wait several weeks

for results

CHORIONIC VILLUS

SAMPLING (CVS)

8-10 weeks gestation Sample extracted from placenta

through vagina/cervix Karyotype in 24 hours

Maternal bleeding Miscarriage

Premature birth Complication rate=2%

Not as invasive as amnio Earlier in gestation

Much quicker results

ULTRA- SOUND

IMAGING

Uses sound waves to produce an image of fetus,

looks like a shadow None known noninvasive

9.10 Explain the ethical dilemmas created by advances in technology. ✍ Can give valuable information to carriers of genetic

disease. ✍ If confidentiality is breached:

o will carriers be stigmatized? o Possibly denied health coverage? o Life insurance? o Denied employment?

✍ Information can be difficult to cope with and strain

marriages. o What should be done about the information? o Termination? o time to prepare emotionally, medically, financially.

9.11 Incomplete Dominance: When the appearance of the F1 offspring falls between the phenotypes of the parents. ✍ Example: Four o’clock flowers

o RR = red o rr = white o Rr = pink

9.12 Multiple alleles: Three alleles per gene present in the population (Two per individual) Example: ABO blood groups Carbohydrates on the surface of RBC’s are recognized by the immune system as “self” or “non-self.” If the carbs are recognized as “non-self” the immune system attacks with antibodies. type A type B type AB type O AA BB AB OO AO BO If you mix the following blood types together, which ones are OK and which ones will be attacked (shaded)? Type AA is done for you. donor AA AO BB BO AB OO

AA OK OK OK AO BB BO AB OO

9.12 Codominance: When both alleles are fully expressed. Which blood type shown above represents codominance?

Which blood type is the universal donor? Which blood type is the universal recipient?


In some animals (horses, cattle, hogs) red hair color is codominant to white. This coat color is called roan. What would you expect to find if you looked at the animal’s coat up close? 9.13 Pleiotropy: A gene affecting multiple characters. Example: Sickle-cell anemia 9.13 Explain how the sickle-cell allele can be adaptive. Sickle-cell Anemia ✍ Due to an allele that makes abnormal hemoglobin ✍ HH normal, Hh = usually normal, hh = suffer ✍ Abnormal hemoglobins tend to link together and crystallize ✍ Crystallization causes RBC to form sickle shape ✍ Can cause severe anemia and weakness ✍ Blood flow limited, causes severe pain, damage to organs ✍ Low oxygen makes it worse ✍ Kills 100,000 people a year globally Sickle-Cell Disease is the most common inherited disorder among people of African descent, 1/400 African-Amer., 1/10 AA is a carrier. Many homozygotes die before they pass on alleles. Why the high frequency of carriers?


Sickle-Cell most common in tropical Africa. Malaria, a parasite of RBC’s, also common there. When parasite enters normal RBC, causes it to sickle. Body destroys sickled/infected cells. Hh are resistant to malaria, more HH die from malaria. Called heterozygote advantage. 9.14 Polygenic inheritance: The additive affects of two or more genes on a single phenotypic character. (This is the converse of pleiotropy, in which a single gene affects several characters.) Whenever a character shows an even gradation between extremes in the population, it is probably due to polygenic inheritance. Below each phenotype, write the genotype(s) that would correspond. Two pairs of genes are (A and a, B and b) are responsible for ear length in corn. They assort independently. Possible phenotypic results are: longest long medium short shortest From the problem above, what would you get if you crossed longest with shortest? Show a Punnett square. 9.15 Explain why skin color is not sufficiently explained by polygenic inheritance. ✍ Skin color is explained by polygenic inheritance. ✍ It is controlled by at least three genes (6 alleles) ✍ This makes seven possible phenotypes. ✍ Can you fit everyone’s skin tone into seven categories? What makes the difference? 9.15 Environment: Many characters result from a combination of heredity and environment. Examples: ✍ human skin color affected by exposure to the sun ✍ human: number of white blood cells affected by altitude,

physical activity, infectious agents. ✍ human height and weight affected by nutrition ✍ tree shape: affected by sun, nutrients, wind 9.17 Linked Genes: Found on the same chromosome. The closer they are on the same chromosome, the less likely they are to get separated by crossing over. So, they are usually inherited together. 9.18 How can crossing over frequency be used to make a gene map of a chromosome? ✍ The closer they are the less often they cross over. ✍ The farther apart they are the more likely they are to cross

over. ✍ If they are more than ½ a chromosome distant, they cross

over 50% of the time, just as often as if they were on separate chromosomes. They assort independently.

Answer: longest x shortest AABB x aabb ab AB AaBb


9.20 Explain how sex is determined in humans. Presence or absence of Y. 9.20 What is the significance of the SRY gene. ✍ SRY=Sex-determining Region of Y. ✍ Triggers testis development. ✍ Codes for proteins that regulate other genes on the Y

chromosome. ✍ These genes produce proteins for normal testis

development. ✍ Absence of SRY in the presence of Y? 9.20 Describe some alternative sex-determination systems Insects (Grasshoppers, roaches, etc):

✍ XO system ✍ Female: XX ✍ Male: X

Fish, Butterflies, Birds: eggs determine sex: ✍ ZW system: ✍ Female: ZW ✍ Male: ZZ

Ants and Bees ✍ No sex chromosomes ✍ Chromosome # ✍ Females: diploid (fertilized eggs) ✍ Males: haploid (unfertilized eggs) ✍ Called: parthenogenesis

9.21 Sex-linked inheritance

✍ Very much like linked genes ✍ Linkage to sex chromosomes only ✍ X usually carries the trait which is absent on the

Y. 9.22 Why do males suffer from sex-linked traits more often than females.

✍ Males inherit more often because they don’t have a second chance (X chromosome) to get a normal allele.

9.23 Explain how the Y chromosome can be used to trace human ancestry.

✍ X and Y are not homologous ✍ No crossing over during Prophase I ✍ Males inherit their Y from dad virtually unchanged ✍ Random changes (neutral mutations) can be

traced back ✍ All males in a certain line will have the changes

honors biology ch. 9 notes “genetics”974029863910305265.weebly.com/uploads/3/0/7/6/3076138/...p...

Documents