Genetics and Meiosis

know how to do punnet squares too they arent included here bc its easier to just find practice problems and theres nothing to remember about them tbh

Heredity

The act of passing genes onto your descendants

Dominance

A allele that displays a phenotype even if only one dominant allele is present.

In pedigrees, the phenotype never skips generations.

Ex: Aa would display the “A“ allele phenotype because the “A“ allele is dominant.

Recessive

A alleles that will only display a phenotype if all alleles are recessive.

In pedigrees, the phenotype can skip generations.

Ex: aa displays the “a“ phenotype, Aa does not display the “a“ phenotype. “a“ must be a recessive allele.

Phenotype

the physical characteristics of an organism displayed based on their genotypes.

Genotype

The physical combination of genes of an organism

Heterozygous

A combination of two different alleles

Ex: Aa is a heterozygous combination.

Homozygous

A combination of two identical alleles

Ex: AA is a homozygous combination.

Allele

Variations on genes that lead to different physical traits. You receive different ones from each parent.

Genes

Segment of DNA that codes for proteins or RNA molecules.

Trait

Characteristics that can be passed hereditarily

mendel’s laws of inheritance: law of dominance

Some alleles are dominant over other alleles.

mendel’s laws of inheritance: law of segregation

Each parent can only provide one allele to each of their descendants.

mendel’s laws of inheritance: law of independent assortment

The assignment of alleles is independent of the other(?)

Ex: in pea plants, the distribution of round vs wrinkled seeds is independent of the distribution between yellow and green seeds.

Mendel’s Experiments

Experiments with pea plants which laid the groundwork for our understanding of genes

Might not need to know the specific term name

Monohybrid crosses

Experiment examining the inheritance of one allele.

Dihybrid Crosses

Experiment examining the inheritance of two different alleles.

Incomplete dominance

The phenotype of a offspring is merely a blend of the dominant alleles from the parents.

Ex: Red and White flowers produce a pink offspring.

Codominance

The offspring displays a simultaneous combination of both dominant alleles from the parents.

Ex: Red and White Flowers produce a offspring with alternating red and white petals

Sex-linked traits

Traits that are passed down specifically based on sex.

This makes it such that pedigrees can reveal sex-related traits if the traits are only present in one sex.

Also makes males more susceptible to sex related illness/trait as their “X“ chromosome only has one copy, thus if a X chromosome has a recessive illness/trait and is passed to a male offspring, the male offspring is guaranteed to have the trait/illness.

Autosomes

Non sex-related chromosones

Human chromosome #

23 pairs, 46 chromosomes

Homologous chromosomes

Pairs of identical coding chromosomes, with each containing a different combination of alleles from each parent.

Pedigree

Family tree that displays the presence of traits across generations

Square in pedigree

Male

Circle in pedigree

female

Dashed/partially filled in pedigree

Carrier

Carrier

An individual who carries a diseased allele but is not afflicted with it. Can pass the disease onto descendants.

Fully filled in on pedigree

Diseased, displays phenotype

Polygenic inheritance

Alleles that are additive and produce different phenotypes based on combinations. Multiple genes determine one phenotype.

Ex: genotypes with aabbcc determine skin color, with the more dominant alleles resulting in darker skin. aabbcc would be the lightest shade, while AABBCC would be the darkest. Combinations of the alleles lead to distinct phenotypes, like AaBbCc leading to a medium shade.

Pleiotrophy

Single gene expresses multiple phenotypes.

Haploid

Containing one set of chromosones. Symbol is n

Diploid

Containing two sets of chromosones, one from each parent. Symbol is 2n

Meiosis I

Replication of chromosomes and genetic diversity promoted by crossing over

Interphase I

Genetic material, one chromatid from each parent, are replicated to form two homologous chromosomes, each containing genetic material from one parent.

Prophase I

Homologous chromosomes crossover to form tetrads, spindle extends from centrioles. The nuclear membrane dissolves.

Tetrads

A pair of homologous chromosomes tightly intertwined during prophase

Metaphase I

Chromosomes line up in the middle of the cell, spindles connect to centromeres

Anaphase I

Spindles begin to retract, pulling the homologous chromosomes apart.

Crossing Over

Process in anaphase I where intertwined homologous chromosomes are pulled apart, diversifying the child with alleles from each parent

Meiosis II

Process identical to mitosis but with haploid gamete cells as both daughter and parent cell

Cells before meiosis I

In Interphase, the gametes are diploid

Cells after meiosis I

After anaphase, the cells are haploid gametes

Cells before and after meiosis II

The cells remain haploid for the entirety of this process.

Synapsis

Intertwining of homologous chromosomes prior to crossing over

Gamete Cells

Haploid sex cells which can combine with other gamete cells to produce a zygote.

Zygote

The first cell of a new organism, made from the fusion of two gamete cells from each parent. It is diploid.

Somatic Cells

Diploid body cells

Telophase I

Chromosomes reach the poles and the nuclear membrane reforms. The sister chromatids still remain attached to form chromosomes, the homologous chromosomes are simply separated with one going into each daughter gamete.

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Telophase II

Anaphase II