Heredity Reading Prompt – 2012 (Holt, pgs. 106 – 113)
Name:_____________________________ Block:_______ Date:________________
Read the paragraphs below and answer the questions below them.
Heredity is the passing of traits from parents to offspring. Inherited traits are characteristics like hair color,
and eye color that form the physical or biological characteristics in a newborn child. Acquired traits are
characteristics that are not inherited from parents like tattoos, scars, or bad hairdos. Those things happen after
you are born, so luckily, can be avoided.
1. What is heredity?________________________________________________________________________
2. What are inherited traits? ___________________________________________________________________
3. How are acquired traits different from inherited traits? ____________________________________________
____________________________________________________________________________________
Gregor Mendel was an Austrian monk who grew vegetables for the monastery garden. He was curious about
how several characteristics of the flowers, pods, seeds, and plants showed up in each generation of pea plants.
He picked peas because from observations, he knew that he could pull off either the male or female flower
parts to control how they were crossed (mated). Through controlled experiments, varying one trait at a time,
he artificially bred plants of one characteristic with those of another to see what the offspring looked like. He
then recorded and analyzed his results. After tens of thousands of experiments, he published his conclusions.
In that way, he followed the scientific method.
4. Why did Mendel experiment with pea plants? _________________________________________________
__________________________________________________________________________________
5. What does the word “crossed” mean? ________________________________________________________
Mendel noticed that some traits showed up most of the time no matter what he crossed. He called those
dominant traits because they seemed to overpower the traits from the other parent. Tallness and purple flowers
seemed dominant. They appeared if only one parent had that characteristic. Recessive traits showed up only
if you crossed 2 rarely seen characteristics, like 2 white flowers or 2 short plants. Those traits seemed to hide
or recede in the background. These conclusions were made from mathematical calculations, not DNA evidence.
The ideas of DNA and genes were not yet proposed. In most modern humans, for the sake of beginner’s genetic
study, brown eyes and dark hair are dominant characteristics.
6. What is a dominant trait? _________________________________________________________________
__________________________________________________________________________________
7. What is a recessive trait? __________________________________________________________________
__________________________________________________________________________________
A gene is one set of instructions for a trait from a single parent (part of a single strand of DNA). The male gene
and female gene must combine as alleles (gene pairs) to develop or express a trait. The dominant gene is
usually represented with a capital letter of the first letter of the dominant characteristic. For example a Purple
pea flower is shown by a “P”. Whenever you see a capital letter it tells you that it only takes one of that gene
from either parent for that dominant trait to show up. The recessive gene is expressed with a lower case letter,
so a White pea flower would be symbolized by a “p”. It takes two recessive genes, one from each parent, for a
recessive trait to appear. It is a “p” not a “w” because the dominant trait is a purple flower.
8. What is a gene? _________________________________________________________________________
9. What is a pair of genes called?________________________
10. How do you show: a dominant gene? __________________ a recessive gene? ___________________
11. How many dominant genes does it take for that trait to show up?________________________________
12. How many recessive genes does it take for that trait to show up?________________________________
A genotype is a simple way to show what gene pairs (alleles) combined to create a single trait in two letters.
A phenotype shows what effect the genotype has in the organism. That effect could be seen physically, like
pea flower color, or hair color. Phenotype could also tell you how an organism might work like basal metabolic
rate, or having a genetic disease like Sickle Cell Anemia.
13. What is a genotype? ____________________________________________________________________
14. What is a phenotype?____________________________________________________________________
15. What is an example of a phenotype?________________________________________________________
Let’s take a look at how genes combine to make genotypes and phenotypes as Mendel did. We will use the
Punnett Square to graphically show the outcome of crossing 2 pea flower genotypes. The father has 2
dominant genes (PP). We can also call that homozygous dominant (“same seed”). The mother has 1
dominant and 1 recessive gene (Pp) or heterozygous (“different seed”). I use an italic or script letter p so I
don’t mistake an uppercase letter for a lowercase one.
♂ P
P
That cross produces 2 homozygous dominant (PP) and 2 heterozygous genotypes for a
genotypic probability of 50% for either. That ratio is based on the statistical likeliness
if you do thousands of similar crosses. All flowers would be pink since each offspring
(block) has at least one dominant P gene, and would have a
phenotypic probability of 100%.
PP PP
Pp Pp
P
♀
p
16. What is a homozygous genotype?___________________________________________________________
17. What is a heterozygous genotype?___________________________________________________________
18. What is a genotypic probability?____________________________________________________________
19. What can you do with a Punnett Square? _____________________________________________________
___________________________________________________________________________________
Tallness (T) is dominant in pea plants. Since pea plants are like vines, growing taller is an advantage by getting
more sunlight. That would make shortness (t) recessive. Below you are to complete 2 Punnett Squares. One
cross (#20) is between 2 heterozygotes (different) or Tt X Tt. The second cross (#21) is between a heterozygous
male with a homozygous recessive female or Tt X tt.
20. Tt X Tt
T ♂
T
♀
t
TT
t
21. Tt X tt
T ♂ t
Genotypes: TT , _____,
t
_____, _____.
♀
Probabilities:____ : _____:___
t
Phenotypes: Tall:_____; Short:______
Probabilities:_______ : _______:_____
Genotypes:____, _____,
_____, _____.
Probabilities:____ : _____ :___
___________
Phenotypes: _______:_____; _______:______
Probabilities:_______ : _______:_____
22. Are ear piercings inherited or acquired traits? _______________ Why?_____________________________
___________________________________________________________________________________
23. What is the difference between dominant and recessive genes? ___________________________________
________________________________________________________________________________________
________________________________________________________________________________________
_________________________________________________________________________________________