GeneticsGenetics

Chapter 10 and Chapter 12Chapter 10 and Chapter 12

VocabularyVocabulary

• 46 Chromosomes in your body cells.• 23 Chromosomes in sperm and eggs.• Sex Chromosomes – X and Y.• Autosomes – all other chromosomes – the

other 22 pairs.• Somatic cells – body cells.• Gametes – sperm and egg.

Intro to the world of GeneticsIntro to the world of Genetics• Genetics – study of heredity• In early 1800’s biologists believed the

blending hypothesis to explain how offspring inherit traits from both parents.

a) Traits – is a characteristic passed from parent to offspring.

b) Heredity – set of characteristics an organism receives from its parents.

Gregor MendelGregor Mendel

• Used experimental approach in science in the 1860’s.

• Austrian monk who’s work gave rise to genetics.

• Father of Heredity• Came up with the theory that

parents pass units of information to offspring called factors (called genes today).

• Studied garden peas1) Grew fast and matured fast2) Produced many offspring3) Male/female on same flower

Mendel’s Big ExperimentsMendel’s Big Experiments•Mendel crossed two plants that were “true breeding” for a particular trait and analyzed the results.

•The P generation = parents•The F1 = 1st offspring•The F2 = F1 X F1•Comparing 1 trait at a time is a monohybrid cross

The Monohybrid Cross – The Monohybrid Cross – Plant HeightPlant Height

• When Mendel crossed 1 tall plant with 1 short plant he found 100% of F1 was tall.

• When Mendel crossed F1 X F1 he found the F2 to be 75% tall and 25% short (3:1 ratio)

Probability Probability • Likelihood that a specific event will

occur.

Number of one kind of possible outcome Total number of all possible outcomes

Mendel Develops Four Mendel Develops Four TheoriesTheories

1) There are alternative forms of genes, for example the gene for plant height in pea plants can be tall or short – these are called alleles

2) Each individual has two alleles for each gene (one from each parent).

1) Homozygous – if each allele is the same – HH or hh – also known as true breeding.2) Heterozygous – if each allele is different – Hh also known as a hybrid.

3) Presence of the alleles does not ensure the trait will be expressed in the individual.1) Dominant – always expressed2) Recessive – present but remains

unexpressed.

• Use letters to represent the alleles of an organism.

• Capital letters mean dominant, lower case letters mean recessive

• Always use the same letter for each gene.

4) Two alleles for a trait are segregated

during the formation of gametes in meiosis.

Theories become Law’s of Theories become Law’s of HeredityHeredity

• Law of Segregation – member of each pair of alleles separates when gametes are formed.

• Law of Independent Assortment – pairs of alleles separate independently of one another during gamete formation.

Genotypes and Genotypes and PhenotypesPhenotypes

• Phenotype – Physical appearance or the observable trait you see in the mirror.

• Genotype – Genetic makeup of an organisms combination of alleles or what’s found in the DNA that you don’t see.

Monohybrid CrossMonohybrid Cross• Cross that

provides data about 1 pair of traits.

• Can predict the outcome by using a Punnett Square

Dihybrid CrossDihybrid Cross• Cross that involves 2 pairs of traits (16

boxes)

Patterns of Heredity Can be ComplexPatterns of Heredity Can be Complex• Incomplete

Inheritance or Incomplete dominance – an individual displays a trait that is intermediate between 2 parents

• Example: Cross between a snapdragon with red flowers and white flowers produces pink flowers)

• Codominance – the dominant alleles are expressed at the same time (roan coat of a horse has both red and white hairs)

• Multiple Alleles – some traits have genes with more than two alleles – expands the possible genotypes and phenotypes of an organism (ABO blood)

• A and B are both dominant over O with is recessive but neither A or B are dominant over the other

• Polygenic Inheritance – a trait that is controlled by more than one pair of genes – combinations of genes (height, weight, body build, hair and skin color)

• Environmental Influences – an individual’s phenotype often depends on conditions in the environment – nutrition (affects height), temperature (affects color of coat), sunlight (affects skin)

• Genetic Linkage – tendency for alleles on one chromosome to be inherited together – the closer the 2 genes on the chromosome the greater the linkage.

• Sex Linked Gene – involves genes on the X chromosome or the Y chromosome. Usually the X because it is a bigger chromosome

Human Genome ProjectHuman Genome Project• 2000 mapped all the genes in DNA

of humans.1) Government funded project2) Evolutionary benefit3) Human Health benefit

Chromosomes Chromosomes AbnormalitiesAbnormalities

• Mutations can happen in any cells but they are not always bad.

1) Source of variations helps species adapt to its environment

2) Chance to improve the organism very slim.

• Types of mutations1) Mutation in chromosomes – involve segments of chromosomes, whole chromosome and even set of chromosome.2) Mutation in genes – occurs in individual genes – may result from change in DNA itself

Genetic DisordersGenetic Disorders

Chromatin to ChromosomesChromatin to Chromosomes

• DNA is found in the nucleus of the cell.

•It is normally in the form of chromatin which is long and stringy.

•When the cell starts to divide the DNA supercoils into chromosomes.

KaryotypeKaryotype• Display of the chromosomes of a cell.• Usually displayed as an arrangement of

chromosome pairs in descending order of size.• Homologous chromosomes are matched up. • Identifies and evaluates the size, shape, and

number of chromosomes in a sample of body cells.

• Extra, missing, or abnormal positions of chromosome pieces can cause problems with a person's growth, development, and body functions.

• 46 chromosomes in body cells (somatic cells) – known as diploid

• 23 chromosomes in gametes – known as haploid.

Normal Male KaryotypeNormal Male Karyotype

Human disorders due to chromosome alterations in autosomes (Chromosomes 1-22). There only 3 trisomies that result in a baby that can survive for a time after birth; the others are too devastating and the baby

usually dies in utero. • Patau syndrome (trisomy 13):

Symptoms Include: serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months.

Nondisjunction of the sex chromosomes (X or Y chromosome):

Can be fatal, but many people have these karyotypes and are just fine!

• Klinefelter syndrome: 47, XXY males. Male sex organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence.

Alterations in chromosome structure: Alterations in chromosome structure: Sometimes, chromosomes Sometimes, chromosomes breakbreak, leading to types of changes in , leading to types of changes in

chromosome structure: Deletion, duplication or translocation (moved)chromosome structure: Deletion, duplication or translocation (moved)

• Cri du Chat (Cry of the cat): A specific deletion of a small portion of chromosome 5; these children have severe mental retardation, a small head with unusual facial features, and a cry that sounds like a distressed cat.

Determining if a genetic Determining if a genetic disorder existsdisorder exists

• Genetic Counseling – pedigree/karyotype – records inheritance patterns over generations.

• Ultrasonography – used to determine the position, sex and if baby is developing normally.

• Amniocentesis – sample fluid surrounding the fetus is withdrawn through a long needle – fluid analyzed.

• Fetoscopy – endoscope inserted through the abdomen – allows direct observation of the fetus – can remove excess fluid from brain of fetus, give blood transfusion, sample skin and blood.