patterns of inheritance unit 6 honors bio (copy)

(o'malley)

**Law of Segregation**

Allele pairs separate during gamete formation and then randomly re-form as pairs during the fusion of gametes during fertilization.

50% of a parents kids get one allele, 50% get the other

meiosis

A two stage cell division exhibited in sexually reproducing organisms that results in the production of gametes(sperm or egg cells).

asexual reproduction

one single parent passes copies of all its genes to its offspring

sexual reproduction

two parents produce offspring with unique combinations of inherited traits

synapsis

during prophase I, homologous chromosomes pair together forming a terad (terad=set of 4)

mitosis

Specifically division of the nucleus during cell division in an organism. Occurs in both sexually and a-sexually reproducing organisms.

crossing over

non-sister chromatids from each homologous chromosome exchange genetic information

If two genes are closer together on the chromosome, more likely to be inherited together during the exchange between the two chromosomes.

oogenesis

the development of egg cells via the process of meiosis in the ovary of a female.

produces one viable egg cell and 3 polar bodies

Females don’t go through meiosis II until after fertilization

Happens since egg cell needs to contain all organelles for celluar function

3 polar bodies are the result of the female rejecting the second X chromosome

**spermatogenesis**

sperm production via meiosis. produces 4 viable sperm cells

Through breeding, Mendel was able to…

establish eight completely dominant traits in pea plants 

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**Law of Independent Assortment**

Each allele pair segregates independently during gamete formation when genes for two different characteristics are located on different pairs of homologous chromosomes…(PUT SIMPLY: Idea that if you take two traits, it doesn’t necessarily mean they will be inherited together if they’re not on the same chromosome)

Just because someone has one trait, doesn’t mean they are automatically going to have another.

Genes are not inherited as a package deal.

nondisjunction

When homologous chromosome pairs during Meiosis I or sister chromatids during Meiosis II do not divide correctly 

monosomy (nondisjunction)

missing one chromosome from a pair

trisomy (nondisjunction)

adding one chromosome to a pair

aneuploid (nondisjunction)

the presence of an extra chromosome or the absence of a chromosome from a pair

autosomes

Any of the chromosomes not involved in determining sex (Chromosome pairs  1-22 in humans)

sex chromosomes

A pair of chromosomes involved in determining sex (Chromosome XY or XX)

karyotype

an individual’s full set of chromosomes…may be used to look for abnormalities in chromosome number or structure.

homologous chromosome pairs

Chromosome pairs that have the same genes containing variations of the same trait…one from mom and one from dad

sister chromatids

Replicated forms of a each homologous chromosome

phenotype

The traits that an organism expresses

alleles

Alternate versions of a gene

dominant allele

the allele that is fully expressed in the phenotype 

recessive allele

the allele that is masked in the phenotype

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epigenetics

Environment can turn genes on/off

Example: identical twins change after time due to certain genes being turned on and off

genotype

The genetic makeup of an organism (ex: AA, aa, Aa)

**Homozygous dominant**

Having two identical dominant alleles for a given trait

**Homozygous recessive**

Having two identical recessive alleles for a given trait

heterozygous

Having a dominant and recessive allele for a given trait.  The dominant allele is expressed as the phenotype.

**Monohybrid Crosses (Complete Dominance)**

A cross between parents which are homozygous for different alleles for the same trait (ex: AA+aa parents) (F1 gen will always be heterozygous)

**Incomplete Dominance**

blend of traits (ex: white+red=pink)

dihybrid crosses

mating between two organisms that are identically hybrid (heterozygous) for two different alleles/traits

sex linked traits

used to observe the inheritance patterns of the sex chromosomes, particularly the X chromosome…most common in males (XY: hemizygous)

**Dosage Compensation (X inactivation)**

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In females only one x-chromosome is acivated in every cell. the inactivated chromosome shrivels up into a barr body. this process is random, and the x chromosome from either the mother or father may be activated

multiple alleles

A genetic trait that has more than three phenotypes (ex: blood types)

antigen

foreign substance that enters the body…can be good if they work with antibodies to “practice” a defense for future invaders (ex: vaccines)

antibody

a protein produced by the immune system to fight off antigens

Rh factor

indicates +/- designation of blood type and whether the blood of two different people is compatible when mixed

multifactoral traits

**involve many genes(polygenic) and many factors (most genes are multifactorial)**

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quantitative traits

measurable phenotype that depends on the cumulative actions of many genes and the environment. (ex: height and weight)

epistasis

one gene altering the expression of another gene

autosomal traits (pedigree)

50/50ish between men and women, can be dominant or recessive

sex-linked traits (pedigree)

more common in males, usually recessive (females can only have it if dad has the trait and mom is a carrier)

In order for mutations to be passed down to future generations, it must occur in the…

gametes (sex cells)…however, this does NOT ALWAYS affect future generations.

Prophase I (Meiosis)

Chromosomes condense

Crossing over occurs

Steps of Meiosis

Prophase I-II, Metaphase I-II, Anaphase I-II, Telophase I-II

NO S Phases

Zygote

Very first cell, merging of sperm and egg cell

Amniocentesis

Amniotic fluid is extracted by the fetus and tested for genetic abnormalities

Chronic Villus Screening

Used to detect anueploidy in babies

done earlier in pregnancy

takes a sample of the mother’s placenta

Law of Dominance

If you put two genes together the offspring will end up with one of them