CHAPTER 4 GENETICS HEREIDTY AND DNA TRAITS Living things inherit traits Traits are the...

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Traits• Living things inherit traits• Traits are the characteristics

you have like hair color and eye color

• Some traits are acquired, not inherited.

• Some are a combination • What are some examples of

acquired traits?

Heredity• Heredity is the passing of genes

from parents to offspring. • We get half our genes from our mom

and half of them from our dad• Genes- is a segment of DNA at a

specific location on chromosome.• We get a random mix of their genes. • “Father of Heredity” is Gregor Mendel

Gregor Mendel • Mendel was born in Austria in 1822Austrian Monk.Austrian Monk.Experimented with Experimented with ““pea plantspea plants””..Used pea plants because:Used pea plants because:They were availableThey were availableThey reproduced quicklyThey reproduced quicklyThey showed obvious differences in They showed obvious differences in the traitsthe traits

Understood that there was Understood that there was something that carried traits something that carried traits from one generation to the from one generation to the next- next- ““FACTORFACTOR””..

Mendel's Plant Breeding Experiments

Gregor Mendel was one of the first to apply an experimental approach to the question of inheritance.

For seven years, Mendel bred pea plants and recorded inheritance patterns in the offspring.

Particulate Hypothesis of Inheritance Parents pass on to their offspring separate and distinct factors (today called genes) that are responsible for inherited traits.

Mendel studies seven characteristics in the garden pea

Mendel observed each trait separately.Mendel started with true-breeding pea plants for each trait.A true breeding plant is one that always produces offspring with a particular trait. Example- a true breeding tall plant will always have tall offspring

Mendel

Identical vs. not identical• Prokaryotes reproduce

Asexually which means their offspring are genetically identical (the same)

• Most Eukaryotes reproduce sexually which means they are a blending of traits. Each offspring gets ½ the genes from mom and ½ the genes from dad.

Genes• DNA wraps around proteins and

compacts (made smaller) to be made into chromosomes.

• Genes are on chromosomes• A gene is a segment of DNA at a

specific location on a chromosome that influences heredity characteristic.

Genes• Each gene has a code for

information that influences a trait.

• Heredity is the passing of genes from parents to offspring.

• Most traits are not coded for by just one gene.

• Some characteristics are affected by many genes.

• In most Eukaryotes, cells contain pairs of chromosomes.

• One chromosome in the pair comes from mom and one comes from dad.

• Humans have 46 chromosomes• Each animal or plant has a specific

# of chromosomes, Chimps have 48 and fruit flies have 8 or 4 pairs.

Chromosomes

Sex chromosomes • In humans, the sex chromosomes

are called the X-chromosome and the Y chromosome

• Females = XX• Males = XY

Human Karyotype

Alleles• Alleles are alternate forms of the

same gene. • For example, there is a gene for

height in pea plants, but they have 2 forms- Tall and Short.

• Alleles can be dominant or recessive.

How Alleles DifferDominant - a term

applied to the trait (allele) that is expressed regardless of the second allele.

Recessive - a term applied to a trait that is only expressed when the second allele is the same (e.g. short plants are homozygous for the recessive allele).

recessive

recessive

recessive

recessive

Alleles Interact to determine traits

Who was the first person to study heredity?

A. Watson and CrickB. Gregor MendelC. Robert HookeD.Louis Pasteur E. Charles Darwin

How many chromosomes do human haves?

A. 23B. 38C. 56D.44E. 46

Genes are located where?

A. On a chromosomeB. In DNAC. PhenotypeD.In our Allele’sE. Dominant

What are alleles?

A. DNAB. ChromosomesC. PhenotypeD.Different form of the

same geneE. Dominant

Girls have what kind of sex chromosomes?

A. XYB. XX

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Phenotype• An organism’s phenotype

describes the actual characteristics that can be observed.

• Example: eye color, hair color, height, size of your feet.

• Any observable trait is part of your phenotype. Blonde hair, green eyes

genotype• Genotype is the name for the

alleles an organism has. • Genotype is your genetic

makeup. • Example: height in pea plants• Phenotype: Tall or Short• Genotype: Tall- TT or Tt Short-

tt (which alleles the plant has)

GenotypesGenotypes RRRR RRrr rrrr

PhenotypesPhenotypesRED RED RED RED YELLOWYELLOW

Types of Genes

• Homozygous- means same genes TT or tt

• You have 100% tall genes if you are a homozygous tall pea plant

• Heterozygous- means different genes Tt, Aa

• You have a mix of both types of genes

Dominant genes• Alleles (a form of a gene) can be

dominant or recessive. • A dominant allele means it is

always expressed if it is present. (but not always when multiple genes code for the same trait)

• Example Pea Plants- the tall allele is dominant so if it is present the plant will always be tall. T= dominant

• TT or Tt = tall plants

Recessive Genes• A recessive allele is one that is

expressed only when two copies are present.

• Example: In pea plants the short allele is recessive

• tt = short plant

Types of Dominance Complete dominance - two alleles code for a

characteristic but only the dominant one is expressed (e.g. you could have alleles for both brown eyes and blue eyes but since brown eyes are dominant over blue eyes, you'll have brown eyes)

Codominance - both alleles are expressed (e.g. a...I dunno - a dog has alleles for both red and black fur. If these alleles are codominant, that means the dog will have a mixture of black and red fur)

Incomplete dominance - neither allele is dominant; the resultant phenotype is a mix of the two (red and white are incompletely dominant with flowers. So if a red and a white flower make more flowers, they would be pink)

Incomplete dominance

CODominance

Color Blindness In Humans: An X-Linked Trait

Sex-Linked Traits: 

1.Normal Color Vision: A: 29,  B: 45,  C: --,  D: 26  

2. Red-Green Color-Blind: A: 70,  B: --,  C: 5,  D: --  

3.Red Color-blind: A: 70,  B: --,  C: 5,  D: 6  

4.Green Color-Blind: A: 70,  B: --,  C: 5,  D: 2

Patterns of Heredity• A punnett square illustrates

how two parents’ alleles might combine in offspring.

• Punnett squares show possible out comes for inheritance.

Punnett squares• Punned squares help scientists

determine probabilities of a trait occurring.

• A probability is the likelihood or chance of a specific outcome.

• If you flip a penny what is the probability that it will land on heads?

What is an organism’s phenotype?

A. Their genesB. Their DNAC. It describes

characteristics that can be observed

D.ChromosomesE. Their personality

What is an organism’s genotype?

A. Their genetic makeup B. Their DNAC. It describes

characteristics that can be observed

D.ChromosomesE. Their personality

Which genes are homozygous?

A. TtB. AaC. TTD.Hair colorE. Zz

A____illustrates how a parent’s alleles might combine?A. CladogramB. Dichotomous KeyC. PictureD.DiagramE. Punnett Square

4.4 D

NA

DNA• DNA is our genetic material that

holds the information for our cells to function.

• DNA is wrapped around proteins to make chromosomes.

• Chromosomes hold our genes which influences hereditary characteristics.

• A gene for height could have different forms (short, tall, etc). These forms are called alleles.

dna• DNA is in the shape of a double

helix (twisted ladder).

The basics of dna• Each side of the ladder is

made up of nucleic acids.• The backbone is a

phosphate and a sugar• The rung of the ladder is

the nitrogen base.

NucleotidesNucleotides

One deoxyribose together with its phosphate and base make a nucleotide.

C C

C

OPhosphate

O

C

C

O -P O

O

O

O -P O

O

O

O -P O

O

O

Nitrogenous base

Deoxyribose

FourFour nitrogenous basesnitrogenous bases

• Cytosine CCytosine C• Thymine TThymine T• Adenine A Adenine A • Guanine GGuanine G

DNA has four different bases:DNA has four different bases:

Two Stranded DNATwo Stranded DNA•Remember, DNA has two Remember, DNA has two strands that fit together strands that fit together something like a zipper.something like a zipper.

ImportantImportant• Adenine and Thymine Adenine and Thymine always join togetheralways join togetherA -- TA -- T• Cytosine and Cytosine and Guanine always join Guanine always join togethertogether C -- GC -- G

Types of nitrogen bases

A= adenineG= guanineC= cytosineT= thymine

Copying DNA

Step 1- DNA unwinds and unzips

Step 2- Once the molecule is separated it copies itself.

The new strand of DNA has bases identical to the original

DNA by the numbersDNA by the numbers•Each cell has about Each cell has about 2 m of DNA.2 m of DNA.•The average human The average human has 75 trillion cells.has 75 trillion cells.•The average human The average human has enough DNA to has enough DNA to go from the earth to go from the earth to the sun more than the sun more than 400 times.400 times.•DNA has a diameter DNA has a diameter of only 0.000000002 of only 0.000000002 m.m.

The earth is 150 billion mThe earth is 150 billion mor 93 million miles from or 93 million miles from the sun.the sun.

What shape is dna?

A. CircleB. HeartC. Double helixD.Regular ladderE. Twisted ladder

What pairs with adenine?

A. CytosineB. ThymineC. GuanineD.NucleotidesE. Adenine

Who discovered the shape of dna?

A. MendelB. PastuerC. HookeD.DarwinE. Watson and Crick

What pairs with Cytosine?

A. CytosineB. ThymineC. GuanineD.NucleotidesE. Adenine