Mol Lecture #24

Question 1

Epistasis

Answer 1

• cases where the effects of one gene are totally dependent on another gene. Usually, one gene can “unmask’ the effect of another.

Question 2

Lab Case ex.

Answer 2

• Start with two true-breeding individuals (unlinked) → cross to get F1 puppies
• Cross F1 with another brown lab to get another ratio: 9:3:4
• The E gene masks effects of the B gene

Question 3

Polygenic Inheritance

Answer 3

• Complex inheritance in humans→ height, eye color (Means: many genes contribute to the phenotype)

Question 4

Polygenic diseases:

Answer 4

• predisposition to cancer, autoimmune disease, cardiovascular disease.
• Cannot do a simple cross with this

Question 5

Pleiotropy

Answer 5

• When 1 gene affects more than one phenotype
• GATA1: transcription factor
  → mutations impact RBC development and independently impact Mast cell

Question 6

Linkage and recombination

Answer 6

• Some genes don’t follow the law of independent assortment and are thus said to be linked because the alleles for the genes always segregate together into the gametes.
• Genes are on the same chromosome.

Question 7

Parental and Recombinant Genotypes

Answer 7

• Test Cross after F1 generation we would expect: 1:1:1:1 ratio
• Received a large number of parental phenotypes, and a small number of others( referred to as recombinants)

Question 8

Parental and Recombinant Genotypes

Answer 8

• Test Cross after F1 generation we would expect: 1:1:1:1 ratio
• Received a large number of parental phenotypes, and a small number of others( referred to as recombinants)

Question 9

Recombination Frequency

Answer 9

• The frequency of recombination is related to how close these genes are.
• Genes that are closer together have a zero chance of recombination, and at some point you cannot tell the difference between linked genes that are really far apart and genes that are on different chromosomes (more than 50 map units apart))

Question 10

Linkage and genetic maps

Answer 10

• Recombination frequency helps with placing genes in order
• Relative map with units in centimorgans or map units (map units correspond to recombination frequency)

Question 11

Pedigrees

Answer 11

• Pedigree charts are graphic representations of the inheritance of a single trait through multiple generations of a family
• Looking at autosomal and sex-linked phenotypes or diseases (narrow biological definitions of sex)

Question 12

X chromosome genetics: Sex determination in humans

Answer 12

• Default development is for an individual to undergo female sexual development (oogenesis) (lots more potential genes on the X chromosome)
• Genes on the Y chromosome cause an individual to undergo male sexual development (spermatogenesis)
• Terms: XX- homogametic / XY- heterogametic

Question 13

X chromosome genetics: Sex determination in humans

Answer 13

• Default development is for an individual to undergo female sexual development (oogenesis) (lots more potential genes on the X chromosome)
• Genes on the Y chromosome cause an individual to undergo male sexual development (spermatogenesis)
• Terms: XX- homogametic / XY- heterogametic

Question 14

Sex Linkage

Answer 14

• For individuals with 2 copies of X, any genes on the X chromosome follow normal mendelian plus inheritance rules
• For hemizygous individuals, they only receive one allele for any gene on the X chromosome.

Question 15

Sex Linkage and disease

Answer 15

• An individual with two X’s has a possibility of being heterozygous or not
• XY can be hemizygous. They only have one copy of X, so they cannot be heterozygous.
• Denoting carrier phenotype.

Question 16

X chromosome inactivation (I)

Answer 16

• Two individuals have different expressions of a protein
• XX individuals have two copies of every X gene. So potentially make 2 X product compared to the same gene for XY individuals.
  –> In order to handle this we inactivate one of the X’s during development (One X is inactivated during development)

Question 17

X chromosome inactivation (II)

Answer 17

• Inactivated X will become something called the Barr body, which is hyper-condensed chromatin.
  –>Barr body is heavily compacted and pushed to the side of the nucleus. The other X functions like all the other chromosomes. (We have some mechanism for letting it out of the Barr body during DNA replication and cell division)

Question 18

Mosaicism

Answer 18

• the random inactivation of x chromosomes during development so that different tissues have a different active X. (cells using one version of an X chromosome for gene expression, while another cell uses the other version)

Question 19

Mosaicism

Answer 19

• the random inactivation of x chromosomes during development so that different tissues have a different active X. (cells using one version of an X chromosome for gene expression, while another cell uses the other version)