Biology Unit 5: Heredity

Karyotype

A picture of all homologous chromosomes arranged in order from largest to smallest.

Homologous Chromosomes

Chromosomes inherited from each parent that carry genes for the same characteristics, same size/banding pattern.

Tetrads

Formed during prophase I, seperate during anaphase I. Hold two sets of chromosomes together.

Meiosis I and II Purpose

Meiosis I results in two haploid cells that consist of two sister chromatids. Meiosis II results in four haploid cells that are genetically distinct.

Prophase I

Chromosomes pair with their homologs and crossing over occurs. Tetrads form.

Metaphase I

Chromosomes line up as homologous pairs, independent assortment occurs.

Anaphase I

Homologous chromosomes seperate

Telophase I

Two haploid cells form which consist of two sister chromatids.

Prophase II

Spindle fibers form, chromosomes are moved by microtubules

Metaphase II

Kinetochores of sister chromatids are attached to microtubules expanding from opposite poles

Anaphase II

Chromatids separate, move towards opposite poles as individual chromosomes

Telophase II

Nuclei form, 4 daughter cells are formed that are genetically different

Crossing Over

When genetic information is exchanged between non sister chromatids, results in 4 unique chromatids in 4 new gametes. New allele combos! Takes place during prophase I.

Independent Assortment

Occurs during metaphase I. Chromosomes line up by homologous pairs in the middle of the cell. Chromosomes line up randomly with maternal and paternal chromosomes mixed on each side of the metaphase plate.

Random Fertilization

Meiosis; unique egg and sperm combine to form unlimited combinations

Somatic Cells

Body cells. Diploid, (2n)

Gametes

Sex cells-haploid (n)

Autosomes

Genes involved in all traits except biological sex. We have 22 pairs.

Sex Chromosomes

Determine biological sex; 1 pair of these.

Haploid

One set of chromosomes, 23 (n)

Diploid

Two sets of chromosomes; 2n

Mendalin Genetics/Complete Dominance

One allele completely masks another

Incomplete Dominance

Heterozygote shows an intermediate phenotype (mixture, ex. red and white make pink)

Codominance

Both alleles are fully expressed (ex. stripes)

Multiple Alleles

More than two alleles exist for a gene in a population

Sex-Lined Inheritence

Genes located on X or Y chromosome

Polygenic Inheritence

Gene controlled by multiple genes

Law of Segregation

During meiosis, homologous chromosomes seperate. Every gamete recieves only one gene per trait. Ex. 2n organisms inherit 2 genes per trait

Law of Independent Assortment

During meiosis, each gene pair assorts independent of other gene pairs on non-homologous chromosomes. Maternal and paternal homologs line up during Meiosis I on the metaphase plate.

Homozygous

HH or hh

Heterozygous

Hh

Allele

Trait given by a parent (h)

Dominant

One trait masks another trait

Recessive

Trait masked by dominant trait

Phenotype

Physical trait

Genotype

Letters representing trait

Locus

Specific location of a gene on a chromosome

Pedigree

Family diagram used to trace inheritence

Sex Chromosomes

Code for biological sex

Autosomes

Other 22 pairs of chromosomes that code for all other genetic traits

Dihybrid Cross

Make multiple monohybrid crosses and multiply probabilities to find overall ratio for traits

Epipstasis

Multiple genes that work together to influence a phenotype. Common in mammal fur color, 3 possibilities of fur color (ex. yellow, chocolate, black).

Pleiotropy

One gene can have multiple phenotypic effects. Multiple symptoms, same gene.

Environmental Effects on Phenotype

Phenotypes dependent on environmental factors like temperature and acidity

Genetic Disorders

-Autosomal recessive: albinism, cystic fibrosis, sickle-cell

-Autosomal Dominant: Huntington’s, dwarfism

-X-Linked Diseases (recessive): Hemophelia, colorblindness

Autosomal Recessive

-trait is rare

-trait skips generations

-trait affects males and females equally

Autosomal Dominant

-trait is found in every generation

-trait is coommon

-equal male and female

X-Linked Dominant

-affected fathers pass to all of their daughters

-males and females are equally likely to be affected

-trait is common

X-Linked Recessive

-trait skips generations

-males are more often affected than females

-affected fathers don’t pass to their sons

-females are carriers

Y-Linked

Allele is found on the Y chromosome-can only be in males.

Linked Genes

Occur when crossing over and independent assortment don’t happen. They are genes on the same chromosome and tend to be inherited together during meiosis. Offspring are identical to parents.

Unliked Genes

Occur when crossing over/independent assortment do occur. New combinations of DNA are made.

1:1:1:1 ratio

Independent assortment, unlinked genes, AaBb * aabb

1:1:0:0

Complete linkage, no crossing over, genes are inherited together, AB/ab * ab/ab

48%: 48%: 2%: 2%

Linked genes, some crossing over, recombinants occur but are rare. AB/ab * ab/ab

3:1:0:0

Complete linkage, only 2 phenotypes, AB/ab * AB/ab

nondisjunction

When chromosomes don’t separate properly in meiosis. Disorders can arise