Bio 110 Ch. 17, 51

Gregor Mendel

Who is known as the father of genetics?

Garden pea plants (Pisum sativum)

What organism did Mendel study?

They show variation, self-fertilize, cross-fertilize easily, and form true-breeding lines

Why were pea plants good for genetics experiments?

One that produces offspring with the same trait over generations

What is a true-breeding organism?

A heritable feature (ex. seed color)

What is a character?

A specific version of a character (ex. yellow or green)

What is a trait?

Seven pairs

How many contrasting traits did Mendel study?

In pollen grains (the stamen)

Where are male gametes produced in peas?

In ovules (the ovary)

Where are female gametes produced?

Fertilization by pollen from the same plant

What is self-fertilization?

Fertilization using pollen from a different plant

What is cross-fertilization?

A cross following one character

What is a monohybrid cross?

Parental generation (true-breeding parents)

What is the P generation?

Offspring of the P generation

What is the F1 generation?

Offspring of F1 self-fertilization

What is the F2 generation?

3 dominant : 1 recessive

What phenotypic ratio appears in the F2 generation?

Traits are dominant and recessive, Genes and alleles, and segregation of alleles

Mendel's three important ideas?

A trait that is expressed when present

What is a dominant trait?

A trait masked by a dominant allele

What is a recessive trait?

A unit of inheritance controlling a character

What is a gene?

Different version of a gene

What are alleles

Two

How many alleles does an individual have per gene?

Alleles separate during gamete formation

What is Mendel's Law of Segregation?

One

How many alleles does each gamete receive?

Genetic makeup (TT, Tt, tt)

What is a genotype?

Physical expression of a trait

What is a phenotype?

Two identical alleles

What does homozygous mean?

Two different alleles

What does heterozygous mean?

Predicting offspring genotypes and phenotypes

What is a Punnett square used for?

1TT : 2Tt : 1 tt

What is the genotype ratio of a Tt x Tt cross?

3 tall: 1 dwarf

What is the phenotype ratio of a Tt x Tt cross?

Crossing a dominant-phenotype individual with a homozygous recessive

What is a testcross?

To determine if the dominant individual is homozygous or heterozygous

Why perform a testcross?

The dominant parent is heterozygous

What if recessive offspring appear?

A cross following two characters

What is a dihybrid cross?

9:3:3:1

What is the typical phenotypic ratio in a dihybrid F2 cross?

Alleles of different genes assort independently

What does independent assortment state?

When genes are linked (close together on the same chromosome)

When does independent assortment NOT apply?

On chromosomes

Where are genes located?

They segregate

What happens to homologous chromosomes during meiosis?

Their behavior during meiosis matches inheritance patterns

how do chromosomes explain Mendel's laws?

A heterozygous individual with a recessive allele

What is a carrier?

Cystic fibrosis

Give an example of a recessive disorder

Huntington's disease

Give an example of a dominant disorder

XX = female, XY = male

What chromosomes determine sex in humans?

A gene located on the X chromosome

What is an X-linked gene?

males have only one X chromosome

Why are X-linked recessive traits more common in males?

Hemophilia, color blindness, Duchenne muscular dystrophy

Examples of X-linked disorders?

Both alleles are fully expressed

What is Codominance?

AB blood type

Example of codominance?

One gene masks another gene's effect

What is epistasis?

A trait controlled by many genes

What is a polygenetic trait?

height, skin color

Examples of polygenetic traits?

It influences how genes are expressed

How does environment affect phenotype?

Reproduction

Biological process producing new individuals of the same species

Development

Series of changes from fertilization to adult form

Gamete

Haploid reproductive cell (sperm or egg)

Fertilization

Fusion of male and female gametes forming a zygote

Zygote

Diploid cell resulting from fertilization, first cell of new organism

Sexual reproduction

Fusion of gametes; increases genetic variation

Asexual reproduction

Offspring arise from one parent; no gamete fusion

Binary Fission

Parent divides into two identical offspring

Budding

New individual grows from parent's body (ex. Hydra)

Fragmentation

Body breaks into pieces that regenerate into new individuals

Parthenogenesis

Development of unfertilized egg into adult (bees, reptiles)

Asexual Advantages

Rapid reproduction; no mate needed; preserves successful traits

Asexual Disadvantages

Low genetic diversity; vulnerable to environmental change

Sexual Advantages

genetic variation; adaptability

Sexual disadvantages

requires energy and mate; slower reproduction

Cleavage

rapid mitotic divisions forming blastula

Blastula

hollow ball of cells after cleavage

Gastrulation

formation of germ layers (ectoderm, mesoderm, and endoderm)

Organogenesis

Development of organs from germ layers

Gonads

Organs producing gametes (testes, ovaries)

Hormones

chemical messengers regulating reproduction (estrogen, testosterone)

External fertilization

gametes released into environment; common in aquatic species

Internal fertilization

gametes unite within body; protects embryo

Ectoderm

outer layer; forms skin and nervous system

Mesoderm

middle layer; forms muscles, bones, and circulatory system

Endoderm

inner layer, forms digestive and respiratory linings

Embryo

Early development stage after zygote divides

Larva

Immature form that undergoes metamorphosis

Oviparous

Eggs laid outside body; embryo develops externally

Viviparous

Embryo develops inside mother; live birth

Ovoviviparous

eggs retained inside mother until hatching

Hermaphroditism

Individual has both male and female reproductive organs

sexual and Asexual reproduction

Comparison of two main reproductive strategies in animals

Gametogenesis and Fertilization

formation of gametes and their union to create a zygote

Human reproductive structures and function

Organs and hormones involved in reproduction

pregnancy and birth in mammals

development of embryo and fetus leading to birth