Unit 5 Heredity

Genetics

the study of heredity and hereditary variation

Heredity

the transmission of traits from one generation to the next

Genes

segments of DNA that code for basic units of heredity

Asexual reproduction

the process by which offspring are produced from a single parent without the involvement of gametes, resulting in genetically identical offspring

Sexual reproduction

the process by which offspring are produced from the combination of gametes from two parents, resulting in genetically diverse offspring

Homologous chromosomes

a pair of chromosomes (same size, length, centromere position) that carry the same genetic information

Karyotypes

a display of chromosome pairs ordered by size and length

Somatic (body) cells

Diploid, or 2n: two complete sets of each chromosome

■ Humans: 2n = 46

Gametic (sex) cells

Haploid, or n: one set of each chromosome

○ Humans (sperm and eggs): n = 23

Autosomes

chromosomes that do not determine sex (humans have 22 pairs)

Sex chromosomes

X and Y

Life cycle

sequence of stages in the reproductive history of an organism from conception to its own reproduction

Meiosis

a process that creates haploid gamete cells in sexually reproducing diploid organisms

Interphase

cell goes through G1, S (DNA is copied), and G2

Synapsis

homologous chromosomes pair up and physically connect to each other forming a tetrad

Crossing over (recombination)

occurs at the chiasmata and DNA is exchanged between the homologous pairs

Prophase I

the first stage of meiosis where homologous chromosomes condense, align, and exchange genetic material through crossing over

Metaphase I

the stage of meiosis where homologous chromosomes are aligned at the cell's equatorial plane before segregation

Anaphase I

the stage of meiosis where homologous chromosomes are pulled apart to opposite poles of the cell

Telophase I and Cytokinesis

the final stage of meiosis I where the separated homologous chromosomes arrive at the poles of the cell and the cytoplasm divides, resulting in two haploid daughter cells

Prophase II

the stage of meiosis II where the chromosomes condense and the nuclear envelope breaks down, preparing for the alignment of chromosomes

Metaphase II

the stage of meiosis II where chromosomes align at the cell's equatorial plane before being separated

Anaphase II

the stage of meiosis II where sister chromatids are pulled apart and move towards opposite poles of the cell

Telophase II and Cytokinesis

the final stages of meiosis II where the chromosomes decondense, the nuclear envelope reforms, and the cytoplasm divides, resulting in four haploid cells

Crossing over

produces recombinant chromosomes: they exchange genetic material

Independent assortment of chromosomes

chromosomes are randomly oriented along the metaphase plate during Metaphase I, each can orient with either the maternal or paternal chromosomes closer to a given pole

Random fertilization

any sperm can fertilize any egg

True breeding

organisms that produce offspring of the same variety over many generations of self pollination

P generation

true-breeding parental generation

F1 generation

(first filial) hybrid offspring of P generation

F2 generation

(second filial) offspring of the F1 generation

Punnett squares

diagrams used to predict the allele combinations of offspring from a cross with known genetic compositions

Homozygous

an organism that has a pair of identical alleles for a character (e.g AA or aa)

Heterozygous

an organism has two different alleles for a gene (e.g Aa)

Genotype

the genetic makeup (alleles) of an organism

Phenotype

an organism’s appearance, which is determined by the genotype

Law of segregation

the two alleles for the same trait separate during gamete formation and end up in different gametes

Alleles

alternative versions of a gene

Monohybrid crosses

a cross between the F1 hybrids

Law of independent assortment

genes for one trait are not inherited with genes of another trait

Dihybrid cross

a cross between F1 dihybrids

The multiplication rule

the probability that two or more independent events will occur together in some specific combination

The addition rule

the probability that two or more mutually exclusive events will occur

Pedigrees

family trees that give a visual of inheritance patterns of particular traits

Incomplete dominance

neither allele is fully dominant (red + white = pink)

Codominance

two alleles that affect phenotype are both expressed

Multiple Alleles

genes that exist in forms with more than two alleles

Epistasis

the phenotypic expression of a gene at one locus affects a gene at another locus

Polygenic inheritance

the effect of two or more genes acting on a single phenotype

Sex-linked gene

a gene located on either the X or the Y chromosome

Y-linked genes

genes specifically found on the Y chromosome

X-linked genes

genes found on the X chromosome

Duchenne muscular dystrophy

progressive weakening of muscles

Hemophilia

inability to properly clot blood

Color blindness

inability to correctly see colors

Barr body

the inactive X in each cell of a female

condenses

Genetic recombination

production of offspring with a new combination of genes from parents

Parental types

offspring with the parental phenotype

Recombinants

offspring with phenotypes that are different from the parents

Linked genes

genes located near each other on the same chromosome that tend to be inherited together

Map units

the distance between genes

Linkage map

genetic map that is based on recombination frequencies

Chi-square

a form of statistical analysis used to compare the actual results (observed) with the expected results

Observed (Actual) values

the numbers that you get in your data

Expected values

based on probability

Phenotypic plasticity

individuals with the same genotype exhibit different phenotypes in different environments

Tay-Sachs disease

autosomal recessive disease, mutated HEXA gene, body fails to produce an enzyme that breaks down a particular lipid

Sickle cell anemia

autosomal recessive disease, mutated HBB gene, sickled cells contain abnormal hemoglobin molecules