Download presentation
Presentation is loading. Please wait.
Published byMorris Reynolds Modified over 9 years ago
1
Chapter 4.1, 4.2C
2
Make a list of the characteristics you see in the 3 children in the picture:
3
4.1: Parents and Offspring are Similar Traits are either: Inherited: traits you get from your parents (hair color, eye color, face shape, etc…) Acquired: developed over your lifetime (learned behaviors, i.e. reading, writing, riding a bike, etc…)
4
Traits are Controlled by Genes Genes: located on chromosomes and code for a particular product (trait) You inherit genes from your parents (heredity) Your cells contain 23 chromosome pairs (homologs) to equal your 46 chromosomes You received half of each homolog from your mother. your father.
5
Traits are Controlled by Genes Each homolog contains sites where genes are located. Though the gene may be present on both, the form of the gene may be different. Alleles: the various forms of the same gene
7
Chromosome Pairs Humans chromosomes are numbered 1- 22; the 23rd pair are the sex chromosomes Sex chromosomes are X-chromosomes and Y-chromosomes Female: XX Male: XY
8
female male
9
Gregor Mendel made some important discoveries about heredity… Performed an experiment with pea plants Discovered that each plant must have two factors for each possible trait, one factor from each parent (Mendel’s “factors” are now known as genes and alleles) Alleles interact to produce traits
10
Alleles Interact to Produce Traits Phenotype: describes your physical characteristics that can be observed (eye color, hair color) Genotype describes the actual genes that you have on your DNA; not always obvious
11
Alleles Interact to Produce Traits Mendel found that we have two copies of each allele (one from mom, one from dad) Alleles can be Dominant Physically expressed regardless of what other allele it is paired with Always expressed as a capital letter (T) (Ex: tallness is the dominant trait for pea plant height) Recessive Physically expressed only when paired with another recessive allele Always expressed as a lower-case letter (t) (Ex: dwarfism is the recessive trait for pea plant height)
12
4.2: Punnett Squares Punnett Squares show possible outcomes for inheritance. Mendel noticed that traits are inherited in patterns. Punnett squares illustrate how the parents’ alleles might combine in offspring. Each parent has two alleles for a particular gene. An offspring receives one allele from each parent. A Punnett square shows how the parents’ alleles may be passed on to potential offspring.
13
Punnett Squares The letter “T”/”t” will refer to height (“T” being tall dominant; “t” being short recessive)
14
Ratios and percentages can express the probability of outcomes Probability: the likelihood or chance of a specific outcome in relation to the total number of possible outcomes Ratio: compares the relationship of two quantities Percentage: a ratio that compares a number to 100
15
Practice… A TT (tall) plant is crossed with a tt (short plant). What is the ratio of tall to short offspring? What percentage of the offspring will be tall?
16
It is important to realize that Punnett squares and probability do not guarantee the outcome of a genetic cross. They indicate the probability of different outcomes. Actual experimental results may not match predicted outcomes.
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.