BIOE 105 Genetics Midterm 1 Review

Rules for x linked dominant

- more females than males will have the trait -all of the daughters, but none of the sons of an affected male will have the trait -one half of the sons and one half of the daughters of an affected female will be affected -the trait is seen in every generation

Rules for X linked recessive

- more males will have the trait -cannot pass from father to son - affected males will pass on the mutation to their daughters who will be carriers -rare affected females will have sons who have the trait and their daughters will be carriers

Rules for Y linked

-only seen in males -all males descended from an affected male will have the trait -females do not exhibit the trait nor do they transmit it

How many Barr bodies would you see in:a XY male? a XX female? a XXY male?a XXX female? a XO female?

0, 1,1,2,0

In a dihybrid cross Y/y; R/r x Y/y; R/r What is the probability of obtaining Y/Y; R/R offspring?

1/16 (1/4 x 1/4)

What is the probability that the progeny of the R/r x R/r cross will be heterozygous?

1/2 ( (1/2 x1/2) dominant from one parent + (1/2 x 1/2) recessive from the other parent)

What is the probability that the progeny in the R/r x R/r cross will be r/r?

1/4 ( 1/2 from one parent, 1/2 from other parent)

In a dihybrid cross Y/y; R/r x Y/y; R/r What is the probability of obtaining Y/y; R/R offspring?

1/8 (1/2 x 1/4)

What % of chromosome 3's would you expect to be gH

10% ( half of the recombinant)

The S and T genes are far apart (i.e. at opposite ends) on chromosome 8. In a population of meiosis events, what % of meiosis events would you expect to have a c.o. (at least 1)between the S and T genes?

100%

Genotypic Ratio of a monohybrid cross

1:2:1

What phenotypic ratio do codominance and incomplete dominance share in a monohybrid cross?

1:2:1

The G and H genes are 20 m.u. apart on chromosome 3.In a population of gametes from a gh/GH individual, what %of chromosome 3's would you expect to be recombinant?

20%

In a cell with D/d, what is its ploidy?

2n

In a dihybrid cross Y/y; R/r x Y/y; R/r What is the probability of obtaining yellow(dom), wrinkled (rec) offspring?

3/16

phenotypic ratio of a monohybrid cross

3:1

The G and H genes are 20 m.u. apart on chromosome 3.In a population of meiosis events from a gh/GH individual,what % of meiosis events would you expect to have a c.o.between the G and H genes?

40%

Roberta and Bob lost their first child to Tay Sachs, a recessive disease. What is the probability that their next two children will not be affected?

9/16

The B and E genes are 10 m.u. apart on chromosome 21.In a population of gametes from a Be/bE individual, what % ofchromosome 21's would you expect to be parental (non-recombinant)?

90%

Codominance

A condition in which both alleles for a gene are fully expressed

aneuploid

Abnormal number of chromosomes.

Haploid

An organism or cell having only one complete set of chromosomes.

homologous chromosomes

Chromosomes that have the same sequence of genes and the same structure

How do you equalize gene dosage?

Compensate for dosage. Mammals transcriptionally inactivate one X chromosome in XX individuals ( Barr body)

The smallest class of recombinants corresponds with what?

Double cross overs

A single E/e; G/g germ cell undergoes nondisjunction in during meiosis I. G and g disjoin normally. What are the 4 genotypes created by this meiosis?

E/e; g E/e; g G G

haplosufficient

For a particular gene, one functioning copy is enough for a wildtype phenotype.

haploinsufficient

For a particular gene, one functioning copy is not enough for a wildtype phenotype.

Which genotypes could be a parent to a child with type A blood?

IA/i, IB/i, i/i, IA/IB

When can we observe crossing over?

In heterozygotes

Barr body

Inactivated X chromosome

Why is a three point cross more accurate than a two point cross?

It accounts for double cross overs.

Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

Joe visited a fertility clinic and was found to have a 44+XXYchromosome composition and to be sterile. What would NOT explain how Joe inherited his unusual set of sex chromosomes?

Nondisjunction in dad during meiosis II

The largest class in a three point cross correspond with what?

Parental genotype

What are parental genotypes in this cross: round x round gives 100% round

R/R x R/-

What genotypes will be present in the F1 generation of : round x round gives 100% round

R/R x R/-

sister chromatids

Replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis or meiosis II.

incomplete dominance

Situation in which one allele is not completely dominant over another allele ( ie red and white make pink)

allelic series

a group of alleles of a gene that display a hierarchy of dominance relationship among them. a collection of variants in which increasingly deleterious mutations lead to increasingly large phenotypic effects

Horizontal patterns of inheritance ( recessive)

affected children can be from two unaffected parents all of the children from two affected parents should be affected

Vertical patterns of inheritance (dominant trait)

affected children have at least one affected parent two affected parents can have unaffected children if they are both heterozygotes

wild type allele

allele present in the population at a >1% frequency

euploid

an individual with the appropriate number of chromosomes for their species

Linked genes

are on the same chromosome and have a recombination frequency of <50%

diploid

containing two complete sets of chromosomes, one from each parent.

mono-hybrid cross

cross between two parents heterozygous for a single gene

dihybrid cross

cross in which two traits are segregating

monomorphic

gene with only one wild type allele

In a D/d cell, D and d are on...?

homologs

n

indicates the ploidy of a cell.

polymorphic gene

multiple genes are wild type

Joe visited a fertility clinic and was found to have a 44+XXYchromosome composition and to be sterile. What could explain how Joe inherited his unusual set of sex chromosomes?

nondisjunction in mom or dad in meiosis I

Ploidy

number of sets of chromosomes in a cell. 2n=diploid, n=haploid

true breeding

progeny looks like parents homozygous for every trait

heterogametic

sex that has two different sex chromosomes

test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

law of independent assortment

the law that states that genes separate independently of one another in meiosis

When is a gene in cis?

when the recessive alleles are on the same chromosome