CHAPTER4GenetiticsandHeredity

CHAPTER 4: GENETICS AND

HEREDITY

• Sexual Reproduction:

Sperm and egg

combine during

fertilization.

• The fertilized egg is

called a zygote.

Diploid Cells

• Two types of cells:

body cells (somatic

cells) or sex cells.

• A diploid cell is a cell

that has pairs of

similar chromosomes.

• A human body cell

Haploid Cells

• Sex cells do not have

pairs of chromosomes so they are haploid.

• They have only have the number of chromosomes as body cells.

• Haploid means single form.

Meiosis and Sex Cells

• Meiosis produces haploid sex cells.

• Meiosis ensures that offspring will have the same diploid number as its parent.

• After 2 haploid sex cells combine, a diploid zygote is produced that develops into a new diploid

Meiosis I

• During meiosis, two

divisions of the nucleus occurs.

• Before meiosis begins, each chromosome is duplicated, just as in mitosis.

• When meiosis is ready to begin, the duplicated

Meiosis II

• The two cells formed

during meiosis I now

begin meiosis II.

• The chromatids of

each duplicated

chromosome will be

separated during this

division.

• When meiosis II is

finished, the

Summary of Meiosis

• Two cells form during

meiosis I. In meiosis

Ii, both of these cells

form two cells.

Comparing Mitosis and Meiosis

• Mitosis occurs in body

cells. Meiosis occurs

in the sex cells.

Mistakes In Meiosis

• Mistakes are more

common in plants than in animals.

• These mistakes can produce cells with too many or too few

chromosomes.

• Sometimes the zygote

produced from these cells dies.

• If the zygote lives, it will have an abnormal

What Is DNA?

• A code that stores hereditary material.

• When a cell divides, the DNA is copied as passed to the new cells.

• New cells receive the same coded information as original cell.

Discovering DNA

• 1950- Rosalind

Franklin discovered

DNA as two chains of

molecules in spiral

form.

• 1953- Watson and

Structure of DNA

• Twisted ladder.

• Each side of the ladder is made up of

sugar-phosphate molecules. • The steps of the ladder

are made up of

nitrogenous bases- adenine, thymine,

cytosine and guanine. • These bases occur in

Copying DNA

• When chromosomes are duplicated before mitosis or meiosis, the amount of DNA in the nucleus is

doubled.

• The two sides of DNA unwind and separate. • Each side then becomes

a pattern on which a new side forms.

Genes

• A gene is a section of DNA on a chromosome. Each chromosome

contains hundreds of genes.

• Genes contain

RNA

• RNA is made in the

nucleus on a DNA

pattern.

• RNA is like a ladder

sawed in half.

• RNA has the bases A,

C, and G like DNA but

has the base uracil

Three Kinds of RNA

• Messenger RNA

(mRNA): begins

protein production.

• Transfer RNA (tRNA):

Bring amino acids to

ribosomes.

The Genetic Code

• Chromosomes are composed mostly of DNA.

• Each chromosome contains thousands of genes.

• The sequence of bases (A, T, C, and G) in a gene forms a code that tells the cell what protein to produce.

• Proteins are made of long chains of amino acids.

• Example: base CGT codes for the amino acid alanine.

How Cells Make Proteins

• Protein Synthesis: production of proteins.

• Protein Synthesis takes place on the

Transcripting the

Code

•DNA molecule unzips between its base pairs.

•One strand of DNA directs production of mRNA.

•RNA pairs of the DNA bases (C with G and U with A)

•mRNA leaves nucleus and enters the cytoplasm.

•mRNA attaches to a ribosome and provides the code for the protein molecule that will form. The

Translating the

Code

•tRNA attaches to mRNA and tRNA reads the

message by pairing up 3-letter codes.

•tRNA carries amino acids that link in a chain in the

order specified by the 3-letter codes.

•Protein molecule continues to grow longer as each tRNA molecule attaches the amino acid it is carrying.

Mutations

• Sometimes mistakes happen when DNA is being copied. • If DNA is not copied exactly,

the proteins made from the instructions might not be made correctly . This can affect a single gene or an entire

chromosome.

• A change in a gene or

chromosome changes the traits of an organism.

HEREDITY

• Heredity is the

passing of traits from

parents to offspring.

• The different forms a

gene may have for a

trait are called alleles.

• Genetics is the study

of how traits are

GREGOR MENDEL: FATHER OF

GENETICS

• Used pea plants to study the way traits are passed from parents to offspring.

• Mendel performed crosses to study seven different

characteristics.

• Mendel crossed plants with round seeds with other plants that produced wrinkled seeds. • First generation of offspring all

had round seed.

TRAITS

• Dominant Trait: a

trait that is expressed

regardless of the

second allele.

• Recessive Trait: a

trait that gets covered

or masked by a

dominant trait. The

trait only appears if

PUNNETT SQUARES

• A tool used to study Mendelian genetics. • Letters are used to

represent dominant and recessive alleles.

• Capital letters for dominant alleles.

• Lower case letters for recessive alleles.

GENOTYPE

• Genetic makeup of an

organism.

• The two genes that

causes a trait.

PHENOTYPE

• The way an organism

looks and behaves.

• The physical

HOMOZYGOUS OR PUREBRED

• Stem word “homo”

means same.

HETEROZYGOUS OR HYBRID

*Stem word “hetero”

means different.

• When there are two

different alleles for

a trait.

MAKING A PUNNETT

SQUARE

1. Determine the

genotypes of the parent organisms.

2. Write down the cross. 3. Draw a Punnett Square. 4. Determine the possible

genotypes of the

offspring by filling in the punnett square.

1. In garden peas, tallness is dominant and shortness is recessive. A purebred or homozygous short pea plant

pollinates a hybrid or heterozygous pea plant.

T = tall

T = short

2. In garden peas, smooth seeds are dominant. Wrinkled seeds are recessive. A purebred or homozygous pea plant

that produces smooth seeds pollinates a pea plant that produces wrinkled seeds.

S = smooth

s = wrinkled

3. The dominant gene F produces freckles in people. A woman and man who are both hybrid or heterozygous for

freckles have several children.

4. In guinea pigs, black fur is dominant over white fur. A white female guinea pig mates with a male guinea pig that

is hybrid or heterozygous for fur color.

B = black

b = white

5. Dimples are dominant in people. A husband and wife both have dimples. The husband is purebred and the wife

is not. The couple have several children.

D = dimples

d = no dimples

PATTERNS OF INHERITANCE

• Incomplete

Dominance: neither

allele for the trait is

dominant.

• The result is an

intermediate

phenotype

PATTERNS OF INHERITANCE

• Multiple Alleles: when a trait is controlled by more than two alleles.

• Traits controlled by

multiple alleles produce more than three

phenotypes of that trait. • Blood type is an example

of multiple alleles that produces four

phenotypes. The alleles for blood are A, B, and O.

GENOTYPES IA_IA

IA_i

RESULTING PHENOTYPES Type A

Type A

IB_IB

IB_i

Type B Type B

IA_IB _{Type AB}

PATTERNS OF INHERITANCE

• Polygenic Inheritance:

When traits are

produced by a

combination of many

genes. This occurs

when a group of gene

pairs acts together to

produce a wide

variety of phenotypes.

• Eye color, skin color,

PATTERNS OF INHERITANCE

• Sex Determination: determined by

chromosomes. • XX = female

• XY = male

• Each egg produced by a female produces only X chromosomes.

PATTERNS OF INHERITANCE

• Sex-linked traits: some

inherited conditions are linked with the X and Y

chromosomes.

• These traits are usually

recessive and exist on the X chromosomes.

• Color-blindness and

hemophilia are sex-linked traits.

• Because males only have one X chromosomes, a male with this allele on his X