Biology Unit 7

gene

segment of DNA that codes for a specific protein, influencing traits

trait

characteristic determined by gene

alleles

different versions of gene

dominant allele

allele that expresses trait even if only 1 copy is present

recessive allele

allele that only shows it’s trait if 2 copies are present

genotype

genetic makeup of an individual

phenotype

physical expression of a trait

homozygous dominant (BB)

2 dominant alleles, shows dominant trait

homozygous recessive (bb)

2 recessive alleles, shows recessive trait

heterozygous (Bb)

1 dominant & 1 recessive allele, expresses dominant trait

somatic cells

body cells (ex. skin, muscle); not involved in reproduction

diploid cells (2n)

cells with 2 sets of chromosomes (one from each parent); found in somatic cells

meiosis

cell division that creates gametes (sex cells) with half the chromosome number

gametes

reproductive cells (sperm & egg) with half the genetic material

haploid cells (n)

cells with one set of chromosomes (ex. gametes)

sex cells

another term of gametes (sperm & egg)

autosomal chromosome

chromosome not involved in determining sex

sex chromosome

chromosome that determine biological sex (XX=female, XY=male)

homologous chromosomes

pair of chromosomes (one from each parent) that have the same genes but may have different alleles

tetrad

a group of 4 chromatids formed when homologous chromosomes pair up during meiosis

law of independent assortment

genes for different traits are inherited separately unless linked

law of segregation

each parent passes only 1 allele for a trait to their offspring

crossing over

exchange of genetic material between homologous chromosomes during meiosis, increasing genetic diversity

purebred (homozygous)

organism with 2 identical alleles for a trait (ex. BB or Bb)

hybrid (heterozygous)

organism with 2 different alleles for a trait (ex. Bb)

P-generation

parent generation in a genetic cross

F1 generation

first generation of offspring from the P-generation

F2 generation

second generation of offspring, produced by crossing F1 individuals

monohybrid cross

genetic cross involving 1 trait (ex. Bb x Bb)

dihybrid cross

genetic cross involving 2 traits (ex. RrYy x RrYy)

incomplete dominance

type of inheritance where heterozygous phenotype is an blend of 2 parent traits, rather than 1 being dominant (RW)

codominance

type of inheritance where both alleles in a heterozygous genotype are fully expressed, without blending (Blood type AB)

sex-linked gene

gene located on sex chromosome, often leading traits that are more common in 1 sex

Law of Dominance

dominant allele masks a recessive allele in heterozygous individuals

Karyotype

picture of all chromosomes in a cell, used to identify genetic disorders and biological sex

Carrier

A person who has one recessive allele for a genetic disorder but does not show symptoms

Antigen

protein on the surface of cells (like red blood cells) that triggers an immune response

Antibody

protein made by the immune system to attack foreign antigens

Complete Dominant Cross

cross where the dominant allele fully masks the recessive one (Bb = dominant trait shows)

Codominant Cross

Both alleles are fully expressed in heterozygous individuals (ex. AB blood type)

Incomplete Dominant Cross

Neither allele is fully dominant, leading to a blended phenotype (Red × White = Pink)