Genetics – the study of heredity

Based on the study of probability(likelihood)

1. Why should we study genetics?

• Disease causes/treatments• Biotechnology – agriculture, animal husbandry • Breeding• Pedigrees- family lineages• Evolutionary trends

1.How are genes passed on to our offspring?

2. Sperm carry ½ and eggs ½ of genetic code.

1. How are sperm & eggs produced?

2. Meiosis – germ cellsdivide to produce haploidcells (1 set of chromosomes)

3. Haploid =1N

2. Meiosis has 2 divisionsto reduce chromosome number

2. What are the phases of meiosis?• Meiosis I– Prophase I- Crossing over of alleles occurs! – Metaphase I- homologous chromosomes side by side– Anaphase I- ho. chrom. separate (not chromatids)– Telophase I- 2 cells with 2 chromatids of every

chromos.

• Meiosis II– Prophase II- nothing happens– Metaphase II- chromo align single file– Anaphase II- chromatids pull apart– Telophase II- 4 total cells w/ 1 copy of each chromo.

1N + 1N = 2N (a diploid cell)

46 XX= female

46 XY = male

23 pr homologouschromosomes

What are the results of meiosis?

• 4 cells• Genetically different• Haploid (1N)• In females, only one egg is used

What happens if chromosomes don’t separate properly?

Nondisjuction results in trisomy or monosomy

Dragon genetics activity to learn basic vocabulary

Check for understanding following activity:

BBBbBbAllele/geneGenotype/phenotype

Mate your dragons

Punnett squares

• Designed to PREDICT outcomes (expected ratios)

Single gene crosses

• monohybrid: Aa x Aa

• Or : AA x Aa

• Or Testcross: aa x A_____

Cystic fibrosis

• Due to a recessive allele (ff)• Faulty membrane protein does not regulate

NaCl• Cells create mucous around them/breeding

ground for bacteria• Chromo #7

Huntington disease

• Due to a dominant allele• Late onset (35 years+)• Protein (huntingtin) destroys nerve cells• Due to a repeat of more than 21 CAG in a

gene• Chromosome 4 (discovered in 1983)• Maracaibo, Venezuela- Huntington research

Di- crosses probability problems

• Rh factors- effect on fetus- protein on RBC- rh from RHESUS monkey- Rh neg makes antibodies against Rh protein-

• Rh is important during fetal development

• Albinism- due to recessive alleles

Review terms

• Alleles/gene• Genotype/phenotype• Homozygous/heterozygous• Probability• Offspring/ F1/F2 generations• Dominant/recessive

Quiz

• 1. Explain how an allele is related to a gene.

• 2. What is the relationship between a genotype and a phenotype?

• 3. Which of the following combinations are homozygous? BB Bb bb

• 4. T-tall t – short Y –yellow y- green• Cross a plant that is heterozygous tall and

homozygous for green seeds with a plant that is short and is also homozygous for green seeds.

• List the genotypes and ratios for the above cross.

• List the phenotypes and ratios for the above cross.

Codominance

• Both alleles of a gene express themselves= both proteins are produced

• Examples:– AB blood type (protein “A” and protein “B”)– Sickle cell trait ( point mutation in hemoglobin)-

produces 3 phenotypes- normal, trait, anemia

Blood type importance

Your immune system makes antibodies against foreign proteins.

Antibody A attacks blood type A Antibody B attacks blood type BAntibodies A & B attack blood type ABAntibodies A & B DO NOT attack blood type O

blood types- multiple alleles

Phenotype (protein)• Blood type A

• Blood type B

• Blood type AB

• Blood type O

Genotype (alleles)• AA or AO

• BB or BO

• AB

• OO

Blood type lab

• Antibodies can cause blood to clump (agglutinate)

• This is how blood is “typed” for accuracy for transfusions.

What is the importance of sickle cell trait?

• Evolutionary advantage to survive Malaria

• “heterozygote” advantage- NS (trait)

• “S” cells sickle and the protozoan is killed

Video clip on sickle cell evolution

http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html

Normal RBCs vs. Sickle RBCs

phenotype• Normal blood cells

• ½ normal & ½ can sickle

• all can sickle

genotype• NN

• NS

• SS

Incomplete dominance

• 2 alleles “blend” their traits and produce a 3rd phenotype

• Examples:– Palamino horses (ncomplete & polygenic)– Tay-Sachs enzyme levels (enzymes, some

enzymes, no enzyme)

Some flowers

X linked genes

• Genes that are located on the X chromosome only

• Examples

– Hemophilia– Red-green color blindness– Duschene muscular dystrophy– Calico cats– ALD (Lorenzo’s oil disease)

hemophilia

• Hemophiliacs lack protein factors for clotting.

Pedigrees

Red – green color blindness

Muscular dystrophy

Image of Calico cat- x linked & epistatic genes

Epistatic genes

• Genes that “cancel” out other genes

Pedigrees

• Family trees that show inheritance

Environmental effects on genes

Polygenic inheritance

• More than one gene codes for a trait

Examples”skin color, eye color, height, hair color

Genes are “additive”

Chromosomal changes

Turner’s Syndrome

Occurs in females. Missing an entire X chromosome.

Non-working ovaries (no menstrual cycle)Short stature and webbed neck Increased risk of heart and cardiovascular

problems

Triple X Syndrome

• Three X chromosomes• Only one X chromosome is active at a time

(little adverse effects)• Tall stature, small head, fold in skin• Learning disabilities. Low self esteem• Fertile

Poly X Syndrome

• XXXX and XXXXX• Similar symptoms to XXX• Small head and jaw• Very tall stature• Irregular shaped heart and lungs• Very low IQ 10-15

Klinefelter Syndrome

• XXY• Common 1:500 male births• Decreased testosterone levels– More female characteristicsDecreased fertilitySlow development as infants and during puberty

XYY Syndrome

• Increased testosterone production– Rapid growth– Large muscle mass (without exercise)– Increased aggression ( still up for debate) – Normal IQ’s and fertile.

XXYY Syndrome

• Similar symptoms to Turners Syndrome but in males

• Mentally Chellenged

XXXY, XXXXY, XXXXXY

• Very rare cases, caused by mutations in the formation of gametes.

• Similar symptoms to Turners Syndrome (extra X).

• Retardation• Short life span• Sterility• Can only be diagnosed with Karyotyping

(what is that?)

timeline

• Genetics introduction to Mendel & vocabulary via dragon genetics

• Single gene Punnetts• Multiple gene Punnetts• Codominance• Incomplete dominance