GENETICS AND HEREDITY

Chapter 5

Genetics and Heredity

Heredity- the passing of traits from parents to offspring

Genetics- the study of how traits are passed from parents to offspring

Gregor Mendel

Considered the Father of GeneticsAustrian MonkHe studied pea plants because they have a

wide variety of traits Pea plants also are readily available and have

a relatively short life spanHe could also control pollination

Mendel Laws

Law of Segregation- each allele separates from the other allele independently

Dominant and Recessive

Dominant- a genetic factor that blocks another genetic factor Only one copy of the gene is necessary for expression of

the trait “Stronger”

Recessive- A genetic factor that is blocked by the presence of a dominant factor Two copies of the trait are necessary for expression of

the trait Hidden, may appear to “skip generations”

Understanding inheritance

Mendel concluded that one gene (factor) from each parent controlled each trait

We know these factors to genes.Genes are located on chromosomesHumans have 46 total or 23 pairs22 pairs are the autosomal chromosomes23 pair determines the sex of the individualMaleXY Female XX

Genes and alleles

Gene- a section on a chromosome that has genetic information for a trait

Allele- the different forms of a gene are called the alleles R- for round r- wrinkled

Genotype and Phenotype

Genotype- the genetic makeupThe two alleles that control the phenotype of the

triat

Phenotype- the physical appearanceHow the trait appears or is expressed

Homozygous and Heterozygous

Homozygous- when the two alleles of the gene are the same RR, rr Purebred

Heterozygous- If the two alleles are different Rr Hybrid

Modeling inheritance

Punnett square- a model used to predict genotypes and phenotypes of the offspring

Pedigree- family tree showing the phenotype of the family members. Can be used to infer genotypes

Complex patterns of inheritance

Incomplete dominance- some traits appear to be a combination of allelesA red flower camellia plant with a white flower camellia only

produces pink flowers

Codominance- When both alleles can be observed in the offspring Cows- both red and white traits

Multiple Alleles- More than two alleles for a trait ABO blood groups

Polygenic inheritance- a combination of many genes and usually some environmental factor (can be unknown) Hair color, skin color, cleft lip, club foot

DNA and Genetics

Genes provide the instruction or blueprint for making an organism

DNA- organisms genetic materialDNA codes for the genesDNA is tightly coiledIt is a double helix structure or twisted

ladder or zipperDiscovered by Watson and Crick

DNA

It is composed of three partsA sugar- deoxyriboseA phosphate groupA nitrogen baseThere are four common nitrogen basesAdenine- (A) pairs with Thymine (T)Cytosine (C) pairs with Guanine (G)

DNA replication

Replication- process of copying a DNA molecule to make another DNA molecule

1. DNA strand separates and nitrogen bases are exposed

2. Nucleotides move in and form new nitrogen bases

3. Two new identical strands are madeAlmost like a zipper opening

Making proteins

Made with the help of Ribonucleic acid (RNA)RNA is single strandedRNA has nitrogen base Uracil (U) rather than

Thymine (T)Sugar is riboseTranscription- making mRNA (messenger

RNA) from DNA

Translation

The process of making proteins from RNA is called translation

There are 2 other types of RNA tRNA- transfer RNA rRNA- ribosomal RNA Translation

tRNA carries amino acids to the proteins mRNA helps form chemical bonds that attach one amino

acid to another The first tRNA separates from its amino acid and mRNA. The cycle continues.

Translating the RNA code

The order of the nitrogen bases in the mRNA determines the order of the amino acids in the protein

Three nitrogen bases are read to pick up the correct amino acid

Three nitrogen bases= codon64 codons but only 20 amino acidsSome code for the same amino acid, some code

for a stop, and some code for the beginning.

Mutations

A mutation is a change in the nucleotide sequence of a gene

Most mutations are corrected during replication

Mutations can be triggered by X-rays, UV light, chemicals, and radioactive materials

Types of mutations

Deletion- one or more nitrogen bases are left out of the DNA sequence

Insertion- one or more nitrogen bases are added to the DNA

Substitution- a nitrogen base is replaced by another different nitrogen base.

Results of mutations

Not all mutations are harmful, some help an organism survive a change in environment

Some will cause a genetic disease or disorder like cystic fibrosis or PKU.