Ch. 16.1: GeneticsMr. Perez

Important Vocabulary Heredity

Allele

Genetics

Hybrid

Dominant

Recessive

Punnett square

Genotype

Phenotype

Homozygous

Heterozygous

Inheriting Traits Heredity: the passing of traits to offspring

An organism is a collection of traits inherited from its parent or parents

What is genetics? Alleles: different forms of a trait that make up a gene

pair When a pair of chromosomes separate during meiosis, the

alleles of a gene pair also separate into different sex cells As a result, every sex cell has one allele for each trait

Genetics: the study of how traits are inherited through the interactions of alleles

http://glencoe.mcgraw-hill.com/sites/0078693918/student_view0/concepts_in_motion.html#

(Click on Meiosis and Fertilization)

Mendel- The Father of Genetics

Gregor Mendel Austrian monk who studied

math and science Became the gardener at a

monastery Predicted the types of flowers

and fruits that would result from crossbreeding two plants

Began experimenting with peas in 1856 Shared results 8 years later

with other scientists

http://science.discovery.com/tv-shows/greatest-discoveries/videos/100-greatest-discoveries-shorts-genetics.htm

Mendel- The Father of Genetics

Mendel was the first scientist to trace one trait through several generations

Genetics in a Garden Each time Mendel studied a plant, he crossed two

plants with different expressions of the trait He found that the new plants all looked like one of the

two parents These new plants were called “hybrids”

Hybrid: receives different genetic information, or different alleles, for a trait from each parent

Purebred: organism that always produces the same traits generation after generation

Dominant and Recessive Factors

Mendel found that tall plants that were crossed with short plants produced seeds that were all tall plants Mendel called the tall form the

“dominant” factor

Dominant: dominates, or covers up, another allele Dominant alleles are written in

capital letters Ex. B = purple flower

Recessive: allele that seems to “disappear” or is covered up Recessive alleles are written in lower

case letters Ex. b = white flower

Using Probability to Make Predictions

Mendel dealt with probabilities His results were more accurate because he worked

with many plants– about 30,000 pea plants! This increased Mendel’s chances of seeing a

repeatable pattern

Punnett square: tool used to predict the results in Mendelian genetics

Punnett Squares In Punnett squares, letters symbolize

alleles Remember, capital letters represent

dominant alleles and lowercase letters represent recessive alleles

The letters form a code for the genetic makeup an organism

Genotype: genetic make up of an organism (BB, Bb, bb)

Phenotype: the way an organism looks and behaves based on their genotype (purple flower or white flower)

Alleles Determine Traits Most cells in your body have

at least two alleles for every trait Located on chromosomes

within each cell’s nucleus

Homozygous: an organism that has two alleles that are the same Example: BB or bb

Heterozygous: an organism that has two different alleles Example: Bb

Making a Punnett Square

Make a grid like this one:

One parent’s alleles are placed on the top, second parent’s alleles place along the side like this (one letter per column/row):

Each square is filled in with one allele donated by each parent.

Make sure the capital (or dominant) allele is placed before the lowercase (or recessive) allele.

In this Punnett square, the probability of each genotype is: BB: 25% or ¼ Bb: 50% or ½ bb: 25% or 1/4

B b

B

b

B b

B BB bB

b bB bb

B b

B BB Bb

b Bb bb

Principles of Heredity It took Mendel years of detailed observation, careful

analysis, and repeated experimentation to conclude his ideas of heredity. The following tables sums them up in three principles:

Video Links http://www.youtube.com/watch?v=xc2wbIDfO7E

http://learn.genetics.utah.edu/content/begin/traits/tour_trait.html

http://learn.genetics.utah.edu/content/begin/traits/tour_heredity.html

Resources• Florida Science Grade 8

Glencoe Science & McGraw Hill Publishing

• Google Images