Unit 5: Heredity

Heredity

The transmission of traits from one generation to the next

Genes

• Segments of DNA that code for proteins

• The basic units of heredity

Mutations

A change in the DNA sequence

Homologous chromosomes

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

• One inherited from mom and one inherited from dad

Asexual reproduction

• Single individual

• No fusion of gametes

• Clone

• Mutations are the only source of variation

• Can reproduce asexually through mitosis

Sexual reproduction

• Two parents (male/female)

• Offspring are unique combinations of genes from parents

• Genetically varied from parents and siblings

Karyotype

A display of chromosome pairs ordered by size and length

Somatic cells

• Body cells

• Diploid

• 2n = 46

Gametic cell

• Sex cells

• haploid

• n = 23

Diploid

Two complete sets of each chromosomes

Haploid

One set of each chromosome

Autosome

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

Sex chromosome

• X and y

• Eggs have an x and sperm either have x or y

Life cycle

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

Zygote

What is formed when a sperm cell fuses with an egg

Genetics

The study of heredity and heredity variation

Clones

Offspring are exact copies of parent

Meiosis

• A process that creates unique, haploids gamete cells in sexually reproducing diploid organisms

• Forms gametes (sperm/egg)

• 2 divisions

• Results in 4 haploid daughter cells

• Each daughter cell is genetically unique

Synapsis

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

• Occurs during prophase I

Tetrad

What is formed when homologous chromosomes pair and connect together in prophase 1

Chiasmata

Where crossing over occurs

Crossing over

• Occurs at the chiasmata

• DNA is exchanged between the homologous pairs

• Every chromatid has a unique combination of DNA

• Occurs during prophase

Independent assortment

• Tetrads line up at the metaphase plate

• Occurs during metaphase I

Meiosis 1

• Starts with 1 diploid cell and ends with 2 unique haploid cells

• Synapsis and crossing over occur in prophase 1

• Tetrads line up at the metaphase plate in metaphase 1

• Homologous pairs separate in anaphase 1

Meiosis II

Starts with 2 unique haploid cells and ends with 4 unique haploid cells

True breeding

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

P generation

True-breeding parental generation

F1 generation

Hybrid offspring of P generation

F2 generation

Offspring of F1 generation

Punnett squares

Diagrams used to predict the allele combinations of offspring from a cross with known genetic composition

Monohybrid cross

• A cross between the F1 hybrids

• Example = Bb x Bb

• Only one trait is being crossed

Dihybrid cross

• A cross between F1 dihybrids

• Example = YrRr x YyRr

• Two traits are being crossed

Phenotype

An organism’s physical appearance, which is determined by the genotype

The Multiplication Rule

The probability that two or more independent events will occur together in some specific combination (this AND that will happen)

Law of segregation

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

Law of independent assortment

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

The Addition Rule

The probability that two or more mutually exclusive events will occur (this OR that will happen)

Recessive alleles

The allele that will only be expressed if a dominant allele is not present

Heterozygous

An organism has two different alleles from a gene

Genotype

The genetic makeup (alleles) of an organism

Dominant

The allele that will be expressed no matter what if it is possessed

Homozygous

An organism that has a pair of identical alleles for a character

Pedigrees

Family trees that gice a visual of inheritance patterns of particuluat traits

Incomplete dominance

• Neither allele is fully dominant

• F1 generation has a phenotype tha tis a mix of the parental generation

Codominacne

Two alleles that affect phenotype are both expressed

Polygenetic inheritance

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

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

X-linked

Genes found the x chromosome

Y-linked

• Genes specifically found on the y chromosome

• There are very few y-linked genes, so their are very few disorders

Hemizygous

When males have only one x chromosome and one y chromosome

Barr body

• The inactive x in each cell of a female condense into this

• Helps to regulate

Recombinants

Offspring with phenotypes that are different from the parents

Linkage map

Genetic map that is based on recombinations frequencies

Chi square

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

Phenotypic plasticity

Individuals with the same genotype exhibit different phenotypes in different environments

Nondisjunction

• Chromosomes fail to separate property in meiosis I or meiosis II

• Karyotyping can detect this

Mitosis

• Occurs in somatic cells

• 1 division

• Results in 2 diploid daughter cells

• Daughter cells are genetically identical

Recombinant chromosomes

Chromosomes that have exchanged genetic material

Allele

Specific sequence of nucleotides that produces a trait

Sex linked genes

A gene located on either the x or the y chromosomes

Duchenne muscular dystrophy

Progressive weakening of muscles