BSCI222 Unit One

gamete

a sex cell formed through meiosis

Mendels First Law

individuals have 2 alleles separated in equal proportions from gamete formation

allele

type of gene with a possible form of variable trait

Mendels Second Law

alleles at different loci separate independent of one another when reproductive cells develop, the allele received at one gamete doesn’t affect allele received at another

monoecious

a species with both male and female reproductive parts

dosage compensation

process of equalizing amounts of protein produced by single X and 2 autosomes

Barr-body formation

one chromosome unused (X)

haplodiploid sex determination

females are diploid and males are haploid (bees)

genic sex determination

genetically determined sex with only genotypes at one or more loci (fungi, fish)

sequential hermaphroditism

a species being both male and female at different times (e.g. mollusk)

temperature dependent sex determination

where incubation temperature overrides chromosomal sex determination (e.g. turtles)

Klinefelter Syndrome (XXY)

cells with 1+ Y chromosomes and multiple X chromosomes

Turner Syndrome (X)

single X chromosome in females

Poly X Female Syndrome (XXX)

too many X

XXY Male Syndrome

incorrect number of X’s

Nondisjunction

homologous chromosomes fail to segregate (anaphase I of MI); 1 cell receives extra, 2nd cell missing

Androgen Insensitivity Syndrome

lacking androgen receptor

X-linked characteristics

genes on X chromosomes for ‘X’ characteristics, recessive traits show in males, dominant allele on X are carriers

autosomal dominant trait

affected parent → affected children, equally likely in men and women

autosomal recessive trait (aa)

when two copies of special gene are required to affect child; skips generation

complete dominance

dominant allele determines phenotype

incomplete dominance

both alleles determine phenotype (phenotype of heterozygote is between homozygotes)

codominance

both alleles determine phenotype (phenotype of heterozygote express phenotype of both homozygotes)

haploinsufficiency

recessive allele where not enough protein is produced in heterozygote (heterozygotes get recessive phenotype)

penetrance

% of individual organisms having a genotype expressing the expected phenotype

expressivity

the degree a trait is expressed

incomplete penetrance

genotype doesn’t always produce expected phenotype

complementation

when two recessive homozygous alleles produce a wild-type phenotype when crossed (eye color in fruit fly)

epistasis

when one gene masks the effect of another gene at a different locus

pleiotropy

when one gene affects many characteristics (Waardenburg syndrome)

polygenic characteristics

continuous traits coded by genes at many loci (height, skin color)

autosomal dominant (Aa)

affected parents → affected kids 50% chance of passing

X linked recessive trait

more likely in males, only passes from mother to son

X linked dominant trait

more likely in females, caused by dominant allele of gene on X chromosome, dad to daughter only

Y linked trait

passed from father to sons only, women never affected

mitochondrial trait

passed from only mother to children (due to egg presence)

An F1 x F1 cross will show a ratio of

3:1