AP Biology Unit 5

heredity

transmission of genes to the next generation

autosomes

chromosomes that do not determine sex; humans have 22

sex chromosomes

chromosomes that determine sex; humans have X and Y

karyotypes

display of chromosome pairs ordered by size and length

meiosis

process that creates four haploid non-identical gamete cells

Prophase I

synapsis and crossing over

synapsis

homologous chromosomes pair up and connect to form a tetrad

crossing over

DNA is exchanged between homologous pairs

tetrad

homologous pairs

Metaphase I

tetrads line up at the metaphase in independent assortment

Anaphase I

homologous pairs separate, not chromatids

chromosome independent assortment

chromosomes randomly oriented along the metaphase

random fertilization

any sperm can fertilize any agg

gene

unit of heredity that codes for a trait

allele

alternative form of a gene

genotype

genetic makeup of an organism

phenotype

observable traits

homozygous

two identical alleles

heterozygous

two different alleles

dominant allele

allele expressed in heterozygotes

recessive allele

allele masked by a dominant allele

mendel

scientist who established laws of inheritance

law of segregation

allele pairs separate during gamete formation

law of independent assortment

genes assort independently if unlinked

Punnett square

diagram predicting genetic outcomes

monohybrid cross

cross involving one trait; follows 3:1 ratio

dihybrid cross

cross involving two traits; follows 9:3:3:1 ratio

pedigrees

family trees that give a visual of inheritance patterns of particular traits

incomplete dominance

heterozygous phenotype is intermediate

codominance

both alleles fully expressed

multiple alleles

more than two alleles for a gene

polygenic trait

trait controlled by multiple genes

epistasis

interaction where one gene affects another

linked genes

genes located close together are more likely to be inherited together

linkage map

genetic map that is based on recombination frequencies

pleiotropy

single gene or mutation influences multiple phenotypic traits

X-linked genes

can be recessive or dominant

Barr body

an inactive X chromosome to prevent over-expression

Y-linked genes

can only be passed to males

non-nuclear inheritance

or maternal inheritance in animals because mitochondria are transmitted by egg

aneuploidy

abnormal chromosome number

autosomal recessive

does not occur in every generation

autosomal dominant

occurs in every generation

Tay-Sachs disease

autosomal recessive; impacts central nervous sytem and blindness

sickle cell anemia

autosomal recessive; abnormal hemoglobin, form sickle shape RBCs

nondisjunction

chromosomes fail to separate properly in meiosis I or II

trisomy 21

three chromosomes in pair 21; results in Down syndrome

phenotypic plasticity

the ability of individual genotypes to produce different phenotypes