Unit 3

Heredity

the transmission of traits from one generation to another

Genetics is the scientific study of

heredity and variation

Genes

units of heredity and made of segments of DNA

Gametes

genes passed to next generation via reproductive cells

Humans have

46 chromosomes

Asexual

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

A Clone is

group of genetically identical individuals from the same parent

Sexual reproduction

two parents give rise to offspring that have unique combinations of genes

Human somatic cells have

23 pairs of chromosomes

Karyotype

ordered display of the pairs of chromosomes from a cell

The sex chromosomes

x and Y

The remaining 22 pairs of chromosomes are

called autosomes

Females

xx

Males are made up of

xy

Homologous chromosomes

includes one chromosome from each parent

46 chromosomes are in

two sets of 23 one from mother one from father

Fertilization

union of gametes

Fertilized egg is called

zygote

The only type of human cells produced by meiosis

gametes

_____ results in one set of chromosomes in each gamete

Meiosis

Exhibit an alternation of generations

Plants and some algae

Diploid organism

called sporophyte and makes haploid spores by meiosis

Spore grows by

mitosis

Chromosomes duplicate

before meiosis

The stages of meiosis

prophase I, metaphase I, anaphase I, telophase I and cytokinesis.

Division of meiosis

prophase II, metaphase II, anaphase II, telophase II and cytokinesis.

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 parent cell.

Mutations

changes in organism’s DNA

Three mechanisms to genetic variation

Independent assortment of chromosomes, crossing over, Random fertilization.

Two laws of inheritance

The law of segregation and the law of independent assortment.

Pleiotrophy

most genes have multiple phenotypic effects.

Epistasis

expression of a gene at one locus alters the phenotypic expression of a gene at a second locus

Traits that depend on multiple genes combined with environmental influences are called

multifactorial

Phenotype

physical appearance, internal anatomy, Physiology and behavior, overall genotype

Pedigree

family tree that describes interrelationships of parents and children across generations

Recessively inherited disorders

show up only in individuals homozygous for the allele

Cystic Fibrosis

most common lethal genetic disease in USA

Sickle cell disease affects

one out of 400 African Americans

In amniocentesis

liquid bathes the fetus is removed and tested

In chorionic villus sampling (CVS)

sample of placenta is removed and tested

Phenylketonuria (PKU)

recessively inherited disorder that occurs in one of every 10,000 -15,000 births in the USA

A gene on the Y chromosome called SRY is responsible for

development of the testes in an embryo

X chromosome contains

1,100 genes

For a recessive X-linked trait to be expressed

a female needs two copies of the allele (homozygous), and a male needs only one copy (hemizygous)

In mammalian females

one of two X chromosomes in each cell is randomly inactivated during embryonic development

Each chromosome other than the Y chromosome

Have hundreds or thousands of genes

Linked genes

genes located on the same chromosome tend to be inherited together

Parental types

offspring with a phenotype matching one of the parental phenotypes

Recombinant types

offspring with nonparental phenotypes

Linkage map

genetic map of chromosome based on recombination frequencies

Large scale chromosomal alterations in humans and other mammals often lead to

spontaneous miscarriages, or lead to disorders

Plants tolerate

genetic changes better than animals

Nondisjunction

pairs of homologous chromosomes do not separate normally during meiosis

Polyploidy

condition in which an organism has more than two complete sets of chromosomes

Polyploidy is more common in

plants