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Transcript of Genetics
Gregor Mendel's studies
The basics of heredity
In this chapter we will learn...
Mendel studied pea plants because they were easy to grow
Pea plants flower and reproduce quickly
Pea plants have many variations
pea plants have only two
He recorded multiple generations
He used true breeding traits
True breeding traits are ones that always produce offspring with that trait.
He took a mathematical approach
He collected mathematical data about the plants
A section of DNA with information on a specific trait is called a
.Each form of a gene with different information is called an
. Mendel called these "factors", not alleles.
Observable traits of an organism, such as eye color and hair color, are called
. Phenotypes are both physical characteristics and things like the way your organs function. The alleles of all the genes on an organism's chromosome make up their
Alleles show incomplete dominance when they produce a blend of the parent's phenotypes. For example, a cross between white and red camellia flowers only produces pink flowers.
When both alleles can be observed in a phenotype, this is called codominance. The blood type AB is an example of this. If you inherit the B allele from one parent and the A allele from the other, you will have type AB blood.
Early ideas about heredity
people used to belive that the genes of the parents mixed together like paint to make a child, but this isn't true
Gregor mendel and his experiments
Gregor Mendel was the first person known to study heredity
He studied genetics in pea plants
Mendel made the laws of heredity
Foundations of genetics
Mendel decided that two factors control each trait
He decided that each gamete-sperm or egg-contributes to each trait
Types of Dominance
Not all allele pairs have a dominant-recessive interaction. Some pairs have more complex interactions such as incomplete dominance, codominance and multiple alleles.
Mendel's experimental Results
Genes and Alleles
Phenotype and Genotype
Mendel's experimental methods
Mendel's unique methods
Mendel was not the first person to conduct breeding experiments on plants, so how was he different?
trait- a specific aspect of an organism, for example, flower color
variation- a difference for a trait, for example,
Dominant and recessive factors
When you cross two true breeding plants you get a hybrid
A dominant factor is one that covers another factor
A recessive factor is one that is covered by another factor
Mendel's Laws of Heredity
Mendel created two hypotheses that showed a pattern in how traits are inherited.
Mendel's law of segregation
This law states that the two factors for each trait separate during meiosis when gametes form.
Mendel's law of Independent assortment
This law means that the factors for one trait separate independently of how factors for other traits separate,and gametes have all possible combinations of traits. As an example, the separation of the two factors for flower color does not affect how the factors for flower position separate, so there are four possible combinations.
The law of segregation
In meiosis 1 replicated chromosomes separate. Then, sister chromatids separate into gametes. Each gamete only receives one allele
Law of Independent assortment
The separation of two factors is separate from the separation for other factors of other traits.the daughter cells receive only one chromosome from each pair of homologous chromosomes.This results in four possible allele combinations for two pairs of homologous chromosomes
Homozygous and Heterozygous genotypes
A genotype for a gene has two alleles
If the two Alleles have the same information (AA or aa) for a gene they are homozygous. If two alleles have different information they are heterozygous.(Aa)
Why do we need to model inheritance?
Modeling inheritance is important because breeders and geneticists can use models to predict the traits of offspring. Also they help us understand why individuals inherit certain traits.
Punnett squares are used to determine the possible genotypes of the offspring when the genotypes of both parents are known.
A pedigree shows traits that are inherited by the members of a family tree. On a pedigree , circles represent female, and squares represent male. Connecting lines show relations between members of the family tree. If a person has inherited the gene, their symbol will be shaded in.
There are two types of punnet square; One trait models and two trait models.
One trait model
One trait models show the out come of two homozygous parents. SInce each parent contributes one R or one r to each of the offspring, they will all be Rr
Two Trait Models
A two trait punnett square is the cross between two parents who are heterozygous. The possible offspring from this cross includes three different genotypes but only two phenotypes.
There are genes that have more than two alleles, or multiple alleles. The human ABO blood group is an example of this. There are three different alleles for the ABO blood type: Ia, Ib and i. Both Ia and Ib are dominant to i. A person can have only two of these alleles, however. They can have these combinations: IaIa, Iai, IbIb, Ibi, ii, or IaIb.
Chromosomes X and Y are the sex chromosomes that determine a person's gender. Each cell in a male has an X chromosome and a Y chromosome, and each cell in a female has two X chromosomes. A recessive phenotype usually is observed only if the genotype is homozygous. However, a recessive phenotype is observed in a male when a one allele gene on his X chromosome has a recessive allele. Therefore males are more likely to have X linked recessive conditions.
Polygenic inheritance is when multiple genes determine the phenotype for a trait. Many phenotypes are possible with polygenic inheritance. The color of horses is one thing that is determined by polygenic inheritance. Height and weight in humans are also influenced by it.
Human genetic disorders
A genetic disorder can result in major health problems throught a person's life. Some common genetic disorders are cystic fibrosis, Huntington's disease, sickle-cell disease, hemophilia and Down syndrome.
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