UAB BY 123 Exam 3

Heredity

the transmission of traits from one generation to the next

Variation

demonstrated by the differences in appearance that offspring show from parents and siblings

Genetics

the scientfic study of heredity and variation

Genes

units of heredity and are made up of segments of DNA

How are genes passed?

Passed to the next generation via reproductive cells called gametes (sperm and eggs)

How is DNA packaged?

into chromosomes

Somatic cells

humans have 46 chromosomes in these cells excpet for gametes

Locus

a gene's specific position along a chromosome

Asexual Reproduction

a single individual passes all of its genes to its offspring without the fusion of gametes

Clone

a group of genetically identical individuals from the same parent

Sexual Reproduction

two parents give rise to offsrping that have unique combinations of genes inhereited from two parents

Hydra budding

a bud develops as an outgrowth due to repeated cell division at one specific site (asexual reproduction)

Life Cycle

the generation-to-generation sequence of stages in the reproductive history of an organism

Zygote

fertilized egg, one set of chromosomes from each parent and produces somatic cells by mitosis and develops into an adult

Karyotype

an ordered display of the pairs of chromosomes from a cell

Homologous Chromosomes

the two chromosomes in each pair, are the same length and shape and carry genes controlling the same inherited characters

Sex Chromosomes

Determine sex of the individual, are called X and Y

Human Females

XX

Human Males

XY

What are the remaining 22 pairs of chromosomes called?

autosomes

Diploid Cell

(2n) two sets of chromosomes

Gamete (Sperm or Egg)

contains a single set of chromosomes and is haploid

Ovum

unfertilized egg, the sex chromosome is X

Sperm

the sex chromosome is either X or Y

Fertilization

the union of gametes (the sperm and the egg)

Sexual Maturity

Ovaries and testes produce haploid cells, only produced by meiosis

Meiosis in Animals

Gametes are the only haploid cell, produced by meiosis and undergo no further cell division before fertilization, gametes fuse to form a diploid zygote that divides by mitosis to develop a multicellular organism

Meiosis in Plants

Exhibit an alternation of generations, life cycle includes botha diploid and haploid multicellular stage

Plant Meiosis

Sporophyte (diploid) makes haploid spores by meiosis then grows by mitosis into gametophyte (haploid)

Meiosis Interphase

chromosomes duplicate, resulting in sister chromatids

Meiosis I

Homologous chromosomes separate, have haploid cells with duplicated chromosomes

Prophase I (Meiosis)

Each chromosome pairs with its homolog and crossing over occurs

Metaphase I (Meiosis)

Pairs line up and microtubules are attached at kinetochore of one chromosome of each tetrad

Cross over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis, only happens in Prophase I

Chiasmata

X-shaped regions where crossing over occurred

Anaphase I (Meiosis)

Pairs of homologous chromosomes separate toward opposite ends

Meiosis II

sister chromatids separate, no DNA replication occurs. Similiar to mitosis

Telophase I (Meiosis)

each half of the cell has a complete haploid set of duplicated chromosomes and each chromosome is composed of two sister chromatids

Prophase II (Meiosis)

spindle apparatus forms and move toward metaphase plate

Metaphase II (Meiosis)

Chromosomes line up at the equator

Anaphase II (Meiosis)

sister chromatids separate

Telophase II (Meiosis)

Cytokinesis occurs, four haploid cells are the result with unreplicated chromosomes

Mitosis vs. Meiosis

Mitosis: conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell

Meiosis: reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell

Events Unique to Meiosis

synapsis and crossing over, homologous pairs at the metaphase plate, separation of homologs

Mutations

Changes in an organisms DNA are original source of genetic diversity

What do mutations create?

different versions of genes called alleles

What produces genetic variation?

reshuffling of alleles during sexual reproduction

What are the three mechanisms contributed to genetic variation?

Independent assortment of chromosomes, crossing over, and random fertilization

Independant Assortment of Chromosomes

Homologous pairs of chromosomes orient randomly at metaphase I, each pair of chromosomes sort maternal and paternal homologs into daughter cells

Number of Chromosome Combinations

2^n (ex. 2^23= over 8 million)

What does crossing over produce?

recombinant chromosomes

Recombinant Chromosomes

Chromosomes that carry genes from each parent and contribute to genetic variation

Random Fertilization

adds to genetic variation because any sperm can fuse with any ovum

Character

a heritable feature that varies among individuals (ex. flower color)

Trait

each variant for a character (ex. purple or white color for flowers)

Advantages for using peas

Short generation time, large number of offspring, mating could be controlled

True-breeding

over many generations of self-pollination, these plants had produced only yhe same variety as the parent plant

Hybridization

Breeding technique that involves crossing dissimilar individuals to bring together the best traits of both organisms

True-breeding Parents

P generation

F1 Generation

hybrid offspring of the P generation

F2 Generation

offspring of the F1 generation

"heitable factor"

gene

Mendel's Model: Concept 1

alternative versions of genes account for variations in inherited characters

Alleles

alternative versions of a gene

Locus

Location of a gene on a chromosome

Mendel's Model: Concept 2

for each character, an organism inherits two alleles, one from each parent

Mendel's Model: Concept 3

If the two alleles at a locus differ, then one (the dominant allele) determines the organism's appearance; the other (the recessive allele) has no noticeable effect on the organism's appearance.

Mendel's Model: Concept 4 (Law of Segregation)

the two alleles for a heritable character seperate (segregate) during gamete formation and end up in different gametes

Punnett Square

A chart that shows all the possible combinations of alleles that can result from a genetic cross

Phenotype

physical appearance

Genotype

genetic makeup

PP and Pp

have the same phenotype (purple flowers) but different genotypes

Testcross

breeding the mystery individual with a homozygous recessive individual

The Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

The Law of Independent Assortment

Each pair of alleles segregates independently of each other pair of alleles during gamete formation

Multiplication Rule

states that the probability that two or more independent events will occur together is the product of their individual probabilities

Addition Rule

states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities

Complete Dominance

occurs when phenotypes of the heterozygote and dominat homozygote are identical

Incomplete Dominance

the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

Codominance

Two dominant alleles affect the phenotype in separate distinguishable ways

Relation Between Dominance and Phenotype

A dominant allele does not subdue a recessive allele; alleles don't interact that way

Alleles are simply variations in a gene's nucleotide sequence

For any character, dominance/recessiveness relationships of alleles depend on the level at which we examine the phenotype

Tay-Sachs disease

fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain

Frequency of Dominant Alleles

Dominant alleles are not necessarily more common in populations than recessive alleles

Pleiotropy

The ability of a single gene to have multiple effects (ex. cystic fibrosis and sickle-cell)

Epistasis

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

Polygenic Inheritance

An additive effect of two or more genes on a single phenotypic character (ex. skin color)

Multifactorial

traits that depend on multiple genes combined with environmental influences

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

Recessively Inherited Disorders

require two copies of the defective gene for the disorder to be expressed (ex. Cystic Fibrosis and Sickle Cell)

Carriers

heterozygous individuals who carry the recessive allele but are phenotypically normal

Dominantly Inherited Disorders

dominant alleles that cause a lethal disease are rare and arise by mutation (ex. Achondroplasia: form of dwarfism)

Multifactoral Disorders

disorders that result from interactions among multiple genes and between genes and the environment (ex. heart disease, diabetes, alcholism, mental illness, cancer)

Chromosomal Theory of Inheritance

-proposed by Sutton and Boveri

-Homologous chromosome pairs are independent of other chromosome pairs

-Parents synthesize gamets that contain only half of their chromosomes

-Gametic chromosomes combine during fertilization to produce offspring with the same chromosome number as their parents

The Chromosomal Basis of Sex

-In humans and other mammals, there are two varieties of sex chromosomes: a larger X chromosome and a smaller Y chromosome

-A person with two X chromosomes develops as a female, while a male develops from a zygote with one X and one Y

-Only the ends of the Y chromosome have regions that are homologous with corresponding regionsof the X chromosome

Inheritance of X-Linked Genes

X chromosomes have genes for many characters unrelated to sex, whereas the Y chromosome mainly encodes genes related to sex determination

disorders caused by recessive alleles on the X chromosome

-Color blindness

-Duchenne muscular dystrophy

-Hemophilia

X Inactivation in Female Mammals

-In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development

-The inactive X condenses into a Barr body

-If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character

Why are linked genes inherited together?

They are located close together on the same chromosome.

How Linkage Affects Inheritance

Linked genes sit close together on a chromosome, making them likely to be inherited together

-Not all genes on a chromosome are linked. Genes that are farther away from one another are more likely to be separated during a process called homologous recombination (when nucleotide sequences are exchanged between two similar or identical molecules of DNA)

Genetic Recombination

The regrouping of genes in an offspring that results in a genetic makeup that is different from that of the parents.