Bio Unit 5: Heredity

monohybrid, dihybrid, trihybrid

mono: crossing two individuals that are hybrid for one gene

di: a genetic mating experiment between two organisms that are both heterozygous for two distinct, unlinked traits

tri: examines the inheritance of three independent traits simultaneously

law of segregation

when alleles for a trait are passed on to an offspring, one is maternal and one is paternal, as a result of the events of meiosis.

law of independent assortment

alleles of different genes get sorted into gametes independently of one another

laws of probability (two formulas: addition and multiplication)

P (A or B) = P(A) + P(B) ——> mutually exclusive

P (A and B) = P(A) x P(B) —→ independent

incomplete dominance

when a heterozygous genotype expresses a phenotype in between the dominant/recessive genotypes

• in incomplete dominance, alleles are written: C^B, C^Y, C^y, etc.

• ex. red, white, and pink flowers

codominance

when both alleles are expressed in a heterozygous offspring

• ex. speckled chickens with black/white patches

incomplete penetrance

• occurs when an expected phenotype fails to appear

• less than 100% of individuals with a certain genotype exhibit it

variable expressivity

when all offspring with a certain genotype exhibit it, but it can appear differently

• normally due to environmental factors

epistasis

when genes infulence each other and seemingly go against independant assortment

• i.e. one gene affects the phenotype of another

• ex. albino gene overrides other fur colors or patterns in animals

sex-linked genes

located on only one chromosome

note: X and Y chromosomes share very few genes in common, and X has roughly 800 genes while Y has roughly 50 (accounts for their size difference)

how males pass genes to offspring

• males transmit X-linked genes to daughter and Y-linked genes to son

• sons inherit X-chromosome from mother

linked genes

genes located physically near each other on a chromosome

• often segregate together in meiosis

map units

• measure genetic linkage on a chromosome, where 1 map unit equals a 1% frequency of recombination

• if 2 linked genes have a recombination frequency of 5%, they are 5 “map units” apart

maternal inheritance & mitochondrial inheritance

• genes inherited from a mother

• egg cell gives organelles to offspring

• therefore, mitochondrial DNA is maternally inherited

paternal inheritance

when organelles transfer from a father to offspring

biparental inheritance

when organelles are inherited from both parents

phenotypic plasticity

ability of a gene to produce multiple phenotypes (mainly a result of environmental variance)

nondisjunction

the failure of chromosomes to separate during meiosis 1 or meiosis 2

• if it happens in meiosis 1, two daughter cells will have no chromosomes and two will have two

• if it happens in meiosis 2, one daughter cell will have no chromosomes, one will have two, and the other two will have the normal amount of 1

four blood types and dominance rules

• types: A, B, AB, O

• A and B are dominant to O

• A and B are codominant to each other

how are genotypes written for blood

I^AI^Bi^O

what is Rh factor

Rh factor is a specific type of antigen on the blood cell

• if you have the positive phenotype, the genotypes are RR or Rr

• the negative phenotype is rr

corresponding blood type phenotypes, genotypes, antigens, and antibodies

diplod vs. haploid + human #’s

diploid is having 2 copies (sister chromatids)

haploid is when you have only one copy

human haploid # is 23, diploid is 46

cells become haploid at the end of meiosis I during telophase/cytokinesis

autosome

all chromosomes besides sex chromosomes

synapsis

aligning genes in crossing over

chiasma

where homologous chromsomes break to exchange genes

review the process of meiosis

fg

gamete

mature haploid cells that are either male or females

zygote

two gametes fuse making a diploid zygote

Oocyte vs. polar bodies and how they are made

in meiosis 1 cytoplasm is divided unevenly. The larger cell once again divides unevenly in meiosis 2. This makes 3 small cells (polar bodies) with disintegrate and one large cell (oocyte) which is the gamete

Meiosis + sperm formation

makes 4 equal sized cells. Most of the cytoplasm is eliminated, making the sperm small