BI111 Lecture Notes - Lecture 1: Mathematical Model, Panmixia, Homologous Chromosome

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27 Jun 2018

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BI111 – L1

Genetics Review (Continued)

Felis Catus: (Cats)

2 alleles

oL (dominant, short hair)

ol (recessive, long hair)

Manx cats

oMutation originated in populations of cats on the Isle of Mann

oTailless mutation is dominant and homozygous lethal

“All white” fur controlled by “white masking” gene

o2 alleles:

W (dominant, all white hair)

w (recessive, colored hair possible)

oW allele has “epistatic”(effects different showing of a phenotype) and “pleiotropic”

(multiple effects in different systems) properties

Another pleiotropic effect on phenotype: sickle cell anemia

The dense pigment gene, D codes for melanophilin, a protein involved in the transportation and

deposition of pigment into a growing hair

o2 alleles:

D - functional melanophilin

d - less-functional melanophilin (dilutes hair colour)

Not all genes are 100% dominant or recessive

oIncomplete or partial dominance:

s (recessive) - homozygous has no white hair (ss)

S (incomplete dominance) - some white hair (sS)

Sex Chromosomes:

The “red” gene, O, located on the X-chromosome determines whether or not there will be red

variation in fur colour

o2 alleles:

O - production of phaeomelanin (red)

o - production of eumelanin (browns and blacks)

oWhat are the possible genotypes?

oPhenotypes?

Homogametic and Heterogametic sex chromosomes

oSex chromosomes often determine sex

oX and Y chromosomes in some species

oXX: female XY: male

oW and Z chromosomes in others (birds)

oWZ: female ZZ: male

Consequences of Sex Chromosomes:

Hetergametic sex has only one copy of each type of sex chromosome

oOne copy of a recessive allele results in expression of the trait

Homogametic sex have 2 copies of sex chromosomes

oHeterozygote: recessive allele hidden (carrier)

oHomozygote recessive: trait expressed

Dosage compensation

oRegulatory process that ensures that males and females have = amounts of X-

chromosomes gene products

oIn female mammals, inactivation of one X chromosome makes the dosage of X-linked

genes the same as males

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Document Summary

L (dominant, short hair) l (recessive, long hair) Manx cats: mutation originated in populations of cats on the isle of mann, tailless mutation is dominant and homozygous lethal. All white fur controlled by white masking gene o. W (recessive, colored hair possible: w allele has epistatic (effects different showing of a phenotype) and pleiotropic (multiple effects in different systems) properties. Another pleiotropic effect on phenotype: sickle cell anemia. The dense pigment gene, d codes for melanophilin, a protein involved in the transportation and deposition of pigment into a growing hair o. D - functional melanophilin d - less-functional melanophilin (dilutes hair colour) Not all genes are 100% dominant or recessive o. Incomplete or partial dominance: s (recessive) - homozygous has no white hair (ss) S (incomplete dominance) - some white hair (ss) The red gene, o, located on the x-chromosome determines whether or not there will be red variation in fur colour o.

Related Questions

___1. Nationally, the most common cause of Down Syndrome is
a. nondisjunction of Chromosome 21 during meiosis
b. translocation of Chromosome 21 onto another chromosome
c. inversion of a large section of Chromosome 21
d. deletion of the Down Syndrome gene
___2. In humans, sex is determined by
a. The presence or absence of the Y chromosome
b. The ratio of X chromosomes to sets of autosomes
c. The temperature during fetal development
d. Which parent is stronger at the time of conception
___3. A translocation is
a. a chromosomal abnormality in which a piece of one chromosome breaks off and attaches to a different chromosome
b. an abnormality in which the chromosomes are translocated out of the nucleus
c. a condition in which the chromosome has broken in two places and come back together with the middle segment backward
d. an abnormality in which there is an extra copy of one chromosome
___ 4. In snapdragons, a red-flowered plant crossed with a white-flowered plant produces all pink-flowered offspring. But crossing two pink-flowered plants produces red, pink, and white in a 1:2:1 ratio. This is a good example of
a. Incomplete dominance
b. Dominance of the red allele over the white allele
c. Lethal effects of the pink allele
d. Sex-linkage of the flower-color alleles
___ 5. If a person with type AB blood marries a person with Type O blood, what blood types are possible in their children? (Assume this trait is a single-gene trait, not complicated by interaction with other genes).
a. A, B, AB, or O
b. A or B only
c. AB or O only
d. AB only 2
___6. In what phase of meiosis are haploid nuclei first formed? a. Anaphase I b. Metaphase II c. Telophase II d. Metaphase I e. Telophase I
___7. What is the phenotype of a heterozygous tall pea plant? a. tall b. Tt c. TT d. tt e. dominant
___ 8. If genes A and B are far apart on a chromosome, and A and C are close together, which of the following observations is expected?
a. Crossing over will occur more often between A and C than between A and B
b. Crossing over will occur at equal frequencies between A and C, and between A and B
c. Crossing over will occur more often between A and B than between A and C
___9. Sometimes an organismâs genotype for one gene masks the effect of a different gene. This phenomenon is called
a. Dominance
b. Incomplete dominance
c. Co-dominance
d. Epistasis
e. Variable expressivity
___10. The dominant allele of a gene is
a. The one that is expressed most often in a population
b. The one that is expressed most often in any particular cross
c. The one that is expressed in an individual that has two different alleles
d. The one that is most healthy to have, that gives the greatest fitness
___11. In human cells, DNA replication occurs
a. In S phase of interphase
b. In G1 phase of interphase
c. In G2 phase of interphase
d. In prophase of mitosis
e. Whenever the cell needs to read the DNA to make proteins
___ 12. A process in which recipient cells take up genes from DNA molecules floating free in the surrounding medium is called
a. conjugation
b. specialized transduction
c. generalized transduction
d. transformation 3
___ 13. Most calico cats are female. However, a few rare males are observed. What is the genotype of a male calico cat?
a. X BX 0
b. X OY
c. X BY
d. X BYY
e. X BX OY
___ 14. A type of red-green color-blindness is a sex-linked (X-linked) recessive trait in humans. Can a woman have this type of color-blindness?
a. Yes, a woman could be color-blind if her mother and father were both heterozygous.
b. Yes, a woman could be color-blind but only if she has an abnormal number of sex chromosomes.
c. No, women can't show sex-linked traits because they lack a Y chromosome.
d. No, women can't show sex-linked traits because they have two X chromosomes.
e. Yes, a woman could be color-blind if her father was color-blind and her mother was a carrier (heterozygous).

BI111 Lecture Notes - Lecture 1: Mathematical Model, Panmixia, Homologous Chromosome

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